text: /**********************************************************************
   * Copyright (c) 2013, 2014 Pieter Wuille                             *
   * Distributed under the MIT software license, see the accompanying   *
   * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
   **********************************************************************/
  
  #ifndef SECP256K1_SCALAR_REPR_IMPL_H
  #define SECP256K1_SCALAR_REPR_IMPL_H
  
  #include "scalar.h"
  #include <string.h>
  
  /* Limbs of the secp256k1 order. */
  #define SECP256K1_N_0 ((uint64_t)0xBFD25E8CD0364141ULL)
  #define SECP256K1_N_1 ((uint64_t)0xBAAEDCE6AF48A03BULL)
  #define SECP256K1_N_2 ((uint64_t)0xFFFFFFFFFFFFFFFEULL)
  #define SECP256K1_N_3 ((uint64_t)0xFFFFFFFFFFFFFFFFULL)
  
  /* Limbs of 2^256 minus the secp256k1 order. */
  #define SECP256K1_N_C_0 (~SECP256K1_N_0 + 1)
  #define SECP256K1_N_C_1 (~SECP256K1_N_1)
  #define SECP256K1_N_C_2 (1)
  
  /* Limbs of half the secp256k1 order. */
  #define SECP256K1_N_H_0 ((uint64_t)0xDFE92F46681B20A0ULL)
  #define SECP256K1_N_H_1 ((uint64_t)0x5D576E7357A4501DULL)
  #define SECP256K1_N_H_2 ((uint64_t)0xFFFFFFFFFFFFFFFFULL)
  #define SECP256K1_N_H_3 ((uint64_t)0x7FFFFFFFFFFFFFFFULL)
  
  SECP256K1_INLINE static void rustsecp256k1zkp_v0_2_0_scalar_clear(rustsecp256k1zkp_v0_2_0_scalar *r) {
      r->d[0] = 0;
      r->d[1] = 0;
      r->d[2] = 0;
      r->d[3] = 0;
  }
  
  SECP256K1_INLINE static void rustsecp256k1zkp_v0_2_0_scalar_set_int(rustsecp256k1zkp_v0_2_0_scalar *r, unsigned int v) {
      r->d[0] = v;
      r->d[1] = 0;
      r->d[2] = 0;
      r->d[3] = 0;
  }
  
  SECP256K1_INLINE static void rustsecp256k1zkp_v0_2_0_scalar_set_u64(rustsecp256k1zkp_v0_2_0_scalar *r, uint64_t v) {
      r->d[0] = v;
      r->d[1] = 0;
      r->d[2] = 0;
      r->d[3] = 0;
  }
  
  SECP256K1_INLINE static unsigned int rustsecp256k1zkp_v0_2_0_scalar_get_bits(const rustsecp256k1zkp_v0_2_0_scalar *a, unsigned int offset, unsigned int count) {
      VERIFY_CHECK((offset + count - 1) >> 6 == offset >> 6);
      return (a->d[offset >> 6] >> (offset & 0x3F)) & ((((uint64_t)1) << count) - 1);
  }
  
  SECP256K1_INLINE static unsigned int rustsecp256k1zkp_v0_2_0_scalar_get_bits_var(const rustsecp256k1zkp_v0_2_0_scalar *a, unsigned int offset, unsigned int count) {
      VERIFY_CHECK(count < 32);
      VERIFY_CHECK(offset + count <= 256);
      if ((offset + count - 1) >> 6 == offset >> 6) {
          return rustsecp256k1zkp_v0_2_0_scalar_get_bits(a, offset, count);
      } else {
          VERIFY_CHECK((offset >> 6) + 1 < 4);
          return ((a->d[offset >> 6] >> (offset & 0x3F)) | (a->d[(offset >> 6) + 1] << (64 - (offset & 0x3F)))) & ((((uint64_t)1) << count) - 1);
      }
  }
  
  SECP256K1_INLINE static int rustsecp256k1zkp_v0_2_0_scalar_check_overflow(const rustsecp256k1zkp_v0_2_0_scalar *a) {
      int yes = 0;
      int no = 0;
      no |= (a->d[3] < SECP256K1_N_3); /* No need for a > check. */
      no |= (a->d[2] < SECP256K1_N_2);
      yes |= (a->d[2] > SECP256K1_N_2) & ~no;
      no |= (a->d[1] < SECP256K1_N_1);
      yes |= (a->d[1] > SECP256K1_N_1) & ~no;
      yes |= (a->d[0] >= SECP256K1_N_0) & ~no;
      return yes;
  }
  
  SECP256K1_INLINE static int rustsecp256k1zkp_v0_2_0_scalar_reduce(rustsecp256k1zkp_v0_2_0_scalar *r, unsigned int overflow) {
      uint128_t t;
      VERIFY_CHECK(overflow <= 1);
      t = (uint128_t)r->d[0] + overflow * SECP256K1_N_C_0;
      r->d[0] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)r->d[1] + overflow * SECP256K1_N_C_1;
      r->d[1] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)r->d[2] + overflow * SECP256K1_N_C_2;
      r->d[2] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint64_t)r->d[3];
      r->d[3] = t & 0xFFFFFFFFFFFFFFFFULL;
      return overflow;
  }
  
  static int rustsecp256k1zkp_v0_2_0_scalar_add(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a, const rustsecp256k1zkp_v0_2_0_scalar *b) {
      int overflow;
      uint128_t t = (uint128_t)a->d[0] + b->d[0];
      r->d[0] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)a->d[1] + b->d[1];
      r->d[1] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)a->d[2] + b->d[2];
      r->d[2] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)a->d[3] + b->d[3];
      r->d[3] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      overflow = t + rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r);
      VERIFY_CHECK(overflow == 0 || overflow == 1);
      rustsecp256k1zkp_v0_2_0_scalar_reduce(r, overflow);
      return overflow;
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_cadd_bit(rustsecp256k1zkp_v0_2_0_scalar *r, unsigned int bit, int flag) {
      uint128_t t;
      VERIFY_CHECK(bit < 256);
      bit += ((uint32_t) flag - 1) & 0x100;  /* forcing (bit >> 6) > 3 makes this a noop */
      t = (uint128_t)r->d[0] + (((uint64_t)((bit >> 6) == 0)) << (bit & 0x3F));
      r->d[0] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)r->d[1] + (((uint64_t)((bit >> 6) == 1)) << (bit & 0x3F));
      r->d[1] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)r->d[2] + (((uint64_t)((bit >> 6) == 2)) << (bit & 0x3F));
      r->d[2] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
      t += (uint128_t)r->d[3] + (((uint64_t)((bit >> 6) == 3)) << (bit & 0x3F));
      r->d[3] = t & 0xFFFFFFFFFFFFFFFFULL;
  #ifdef VERIFY
      VERIFY_CHECK((t >> 64) == 0);
      VERIFY_CHECK(rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r) == 0);
  #endif
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_set_b32(rustsecp256k1zkp_v0_2_0_scalar *r, const unsigned char *b32, int *overflow) {
      int over;
      r->d[0] = (uint64_t)b32[31] | (uint64_t)b32[30] << 8 | (uint64_t)b32[29] << 16 | (uint64_t)b32[28] << 24 | (uint64_t)b32[27] << 32 | (uint64_t)b32[26] << 40 | (uint64_t)b32[25] << 48 | (uint64_t)b32[24] << 56;
      r->d[1] = (uint64_t)b32[23] | (uint64_t)b32[22] << 8 | (uint64_t)b32[21] << 16 | (uint64_t)b32[20] << 24 | (uint64_t)b32[19] << 32 | (uint64_t)b32[18] << 40 | (uint64_t)b32[17] << 48 | (uint64_t)b32[16] << 56;
      r->d[2] = (uint64_t)b32[15] | (uint64_t)b32[14] << 8 | (uint64_t)b32[13] << 16 | (uint64_t)b32[12] << 24 | (uint64_t)b32[11] << 32 | (uint64_t)b32[10] << 40 | (uint64_t)b32[9] << 48 | (uint64_t)b32[8] << 56;
      r->d[3] = (uint64_t)b32[7] | (uint64_t)b32[6] << 8 | (uint64_t)b32[5] << 16 | (uint64_t)b32[4] << 24 | (uint64_t)b32[3] << 32 | (uint64_t)b32[2] << 40 | (uint64_t)b32[1] << 48 | (uint64_t)b32[0] << 56;
      over = rustsecp256k1zkp_v0_2_0_scalar_reduce(r, rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r));
      if (overflow) {
          *overflow = over;
      }
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_get_b32(unsigned char *bin, const rustsecp256k1zkp_v0_2_0_scalar* a) {
      bin[0] = a->d[3] >> 56; bin[1] = a->d[3] >> 48; bin[2] = a->d[3] >> 40; bin[3] = a->d[3] >> 32; bin[4] = a->d[3] >> 24; bin[5] = a->d[3] >> 16; bin[6] = a->d[3] >> 8; bin[7] = a->d[3];
      bin[8] = a->d[2] >> 56; bin[9] = a->d[2] >> 48; bin[10] = a->d[2] >> 40; bin[11] = a->d[2] >> 32; bin[12] = a->d[2] >> 24; bin[13] = a->d[2] >> 16; bin[14] = a->d[2] >> 8; bin[15] = a->d[2];
      bin[16] = a->d[1] >> 56; bin[17] = a->d[1] >> 48; bin[18] = a->d[1] >> 40; bin[19] = a->d[1] >> 32; bin[20] = a->d[1] >> 24; bin[21] = a->d[1] >> 16; bin[22] = a->d[1] >> 8; bin[23] = a->d[1];
      bin[24] = a->d[0] >> 56; bin[25] = a->d[0] >> 48; bin[26] = a->d[0] >> 40; bin[27] = a->d[0] >> 32; bin[28] = a->d[0] >> 24; bin[29] = a->d[0] >> 16; bin[30] = a->d[0] >> 8; bin[31] = a->d[0];
  }
  
  SECP256K1_INLINE static int rustsecp256k1zkp_v0_2_0_scalar_is_zero(const rustsecp256k1zkp_v0_2_0_scalar *a) {
      return (a->d[0] | a->d[1] | a->d[2] | a->d[3]) == 0;
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_negate(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a) {
      uint64_t nonzero = 0xFFFFFFFFFFFFFFFFULL * (rustsecp256k1zkp_v0_2_0_scalar_is_zero(a) == 0);
      uint128_t t = (uint128_t)(~a->d[0]) + SECP256K1_N_0 + 1;
      r->d[0] = t & nonzero; t >>= 64;
      t += (uint128_t)(~a->d[1]) + SECP256K1_N_1;
      r->d[1] = t & nonzero; t >>= 64;
      t += (uint128_t)(~a->d[2]) + SECP256K1_N_2;
      r->d[2] = t & nonzero; t >>= 64;
      t += (uint128_t)(~a->d[3]) + SECP256K1_N_3;
      r->d[3] = t & nonzero;
  }
  
  SECP256K1_INLINE static int rustsecp256k1zkp_v0_2_0_scalar_is_one(const rustsecp256k1zkp_v0_2_0_scalar *a) {
      return ((a->d[0] ^ 1) | a->d[1] | a->d[2] | a->d[3]) == 0;
  }
  
  static int rustsecp256k1zkp_v0_2_0_scalar_is_high(const rustsecp256k1zkp_v0_2_0_scalar *a) {
      int yes = 0;
      int no = 0;
      no |= (a->d[3] < SECP256K1_N_H_3);
      yes |= (a->d[3] > SECP256K1_N_H_3) & ~no;
      no |= (a->d[2] < SECP256K1_N_H_2) & ~yes; /* No need for a > check. */
      no |= (a->d[1] < SECP256K1_N_H_1) & ~yes;
      yes |= (a->d[1] > SECP256K1_N_H_1) & ~no;
      yes |= (a->d[0] > SECP256K1_N_H_0) & ~no;
      return yes;
  }
  
  static int rustsecp256k1zkp_v0_2_0_scalar_cond_negate(rustsecp256k1zkp_v0_2_0_scalar *r, int flag) {
      /* If we are flag = 0, mask = 00...00 and this is a no-op;
       * if we are flag = 1, mask = 11...11 and this is identical to rustsecp256k1zkp_v0_2_0_scalar_negate */
      uint64_t mask = !flag - 1;
      uint64_t nonzero = (rustsecp256k1zkp_v0_2_0_scalar_is_zero(r) != 0) - 1;
      uint128_t t = (uint128_t)(r->d[0] ^ mask) + ((SECP256K1_N_0 + 1) & mask);
      r->d[0] = t & nonzero; t >>= 64;
      t += (uint128_t)(r->d[1] ^ mask) + (SECP256K1_N_1 & mask);
      r->d[1] = t & nonzero; t >>= 64;
      t += (uint128_t)(r->d[2] ^ mask) + (SECP256K1_N_2 & mask);
      r->d[2] = t & nonzero; t >>= 64;
      t += (uint128_t)(r->d[3] ^ mask) + (SECP256K1_N_3 & mask);
      r->d[3] = t & nonzero;
      return 2 * (mask == 0) - 1;
  }
  
  /* Inspired by the macros in OpenSSL's crypto/bn/asm/x86_64-gcc.c. */
  
  /** Add a*b to the number defined by (c0,c1,c2). c2 must never overflow. */
  #define muladd(a,b) { \
      uint64_t tl, th; \
      { \
          uint128_t t = (uint128_t)a * b; \
          th = t >> 64;         /* at most 0xFFFFFFFFFFFFFFFE */ \
          tl = t; \
      } \
      c0 += tl;                 /* overflow is handled on the next line */ \
      th += (c0 < tl);          /* at most 0xFFFFFFFFFFFFFFFF */ \
      c1 += th;                 /* overflow is handled on the next line */ \
      c2 += (c1 < th);          /* never overflows by contract (verified in the next line) */ \
      VERIFY_CHECK((c1 >= th) || (c2 != 0)); \
  }
  
  /** Add a*b to the number defined by (c0,c1). c1 must never overflow. */
  #define muladd_fast(a,b) { \
      uint64_t tl, th; \
      { \
          uint128_t t = (uint128_t)a * b; \
          th = t >> 64;         /* at most 0xFFFFFFFFFFFFFFFE */ \
          tl = t; \
      } \
      c0 += tl;                 /* overflow is handled on the next line */ \
      th += (c0 < tl);          /* at most 0xFFFFFFFFFFFFFFFF */ \
      c1 += th;                 /* never overflows by contract (verified in the next line) */ \
      VERIFY_CHECK(c1 >= th); \
  }
  
  /** Add 2*a*b to the number defined by (c0,c1,c2). c2 must never overflow. */
  #define muladd2(a,b) { \
      uint64_t tl, th, th2, tl2; \
      { \
          uint128_t t = (uint128_t)a * b; \
          th = t >> 64;               /* at most 0xFFFFFFFFFFFFFFFE */ \
          tl = t; \
      } \
      th2 = th + th;                  /* at most 0xFFFFFFFFFFFFFFFE (in case th was 0x7FFFFFFFFFFFFFFF) */ \
      c2 += (th2 < th);               /* never overflows by contract (verified the next line) */ \
      VERIFY_CHECK((th2 >= th) || (c2 != 0)); \
      tl2 = tl + tl;                  /* at most 0xFFFFFFFFFFFFFFFE (in case the lowest 63 bits of tl were 0x7FFFFFFFFFFFFFFF) */ \
      th2 += (tl2 < tl);              /* at most 0xFFFFFFFFFFFFFFFF */ \
      c0 += tl2;                      /* overflow is handled on the next line */ \
      th2 += (c0 < tl2);              /* second overflow is handled on the next line */ \
      c2 += (c0 < tl2) & (th2 == 0);  /* never overflows by contract (verified the next line) */ \
      VERIFY_CHECK((c0 >= tl2) || (th2 != 0) || (c2 != 0)); \
      c1 += th2;                      /* overflow is handled on the next line */ \
      c2 += (c1 < th2);               /* never overflows by contract (verified the next line) */ \
      VERIFY_CHECK((c1 >= th2) || (c2 != 0)); \
  }
  
  /** Add a to the number defined by (c0,c1,c2). c2 must never overflow. */
  #define sumadd(a) { \
      unsigned int over; \
      c0 += (a);                  /* overflow is handled on the next line */ \
      over = (c0 < (a));         \
      c1 += over;                 /* overflow is handled on the next line */ \
      c2 += (c1 < over);          /* never overflows by contract */ \
  }
  
  /** Add a to the number defined by (c0,c1). c1 must never overflow, c2 must be zero. */
  #define sumadd_fast(a) { \
      c0 += (a);                 /* overflow is handled on the next line */ \
      c1 += (c0 < (a));          /* never overflows by contract (verified the next line) */ \
      VERIFY_CHECK((c1 != 0) | (c0 >= (a))); \
      VERIFY_CHECK(c2 == 0); \
  }
  
  /** Extract the lowest 64 bits of (c0,c1,c2) into n, and left shift the number 64 bits. */
  #define extract(n) { \
      (n) = c0; \
      c0 = c1; \
      c1 = c2; \
      c2 = 0; \
  }
  
  /** Extract the lowest 64 bits of (c0,c1,c2) into n, and left shift the number 64 bits. c2 is required to be zero. */
  #define extract_fast(n) { \
      (n) = c0; \
      c0 = c1; \
      c1 = 0; \
      VERIFY_CHECK(c2 == 0); \
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_reduce_512(rustsecp256k1zkp_v0_2_0_scalar *r, const uint64_t *l) {
  #ifdef USE_ASM_X86_64
      /* Reduce 512 bits into 385. */
      uint64_t m0, m1, m2, m3, m4, m5, m6;
      uint64_t p0, p1, p2, p3, p4;
      uint64_t c;
  
      __asm__ __volatile__(
      /* Preload. */
      "movq 32(%%rsi), %%r11\n"
      "movq 40(%%rsi), %%r12\n"
      "movq 48(%%rsi), %%r13\n"
      "movq 56(%%rsi), %%r14\n"
      /* Initialize r8,r9,r10 */
      "movq 0(%%rsi), %%r8\n"
      "xorq %%r9, %%r9\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9) += n0 * c0 */
      "movq %8, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      /* extract m0 */
      "movq %%r8, %q0\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10) += l1 */
      "addq 8(%%rsi), %%r9\n"
      "adcq $0, %%r10\n"
      /* (r9,r10,r8) += n1 * c0 */
      "movq %8, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += n0 * c1 */
      "movq %9, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* extract m1 */
      "movq %%r9, %q1\n"
      "xorq %%r9, %%r9\n"
      /* (r10,r8,r9) += l2 */
      "addq 16(%%rsi), %%r10\n"
      "adcq $0, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += n2 * c0 */
      "movq %8, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += n1 * c1 */
      "movq %9, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += n0 */
      "addq %%r11, %%r10\n"
      "adcq $0, %%r8\n"
      "adcq $0, %%r9\n"
      /* extract m2 */
      "movq %%r10, %q2\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9,r10) += l3 */
      "addq 24(%%rsi), %%r8\n"
      "adcq $0, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += n3 * c0 */
      "movq %8, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += n2 * c1 */
      "movq %9, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += n1 */
      "addq %%r12, %%r8\n"
      "adcq $0, %%r9\n"
      "adcq $0, %%r10\n"
      /* extract m3 */
      "movq %%r8, %q3\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10,r8) += n3 * c1 */
      "movq %9, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += n2 */
      "addq %%r13, %%r9\n"
      "adcq $0, %%r10\n"
      "adcq $0, %%r8\n"
      /* extract m4 */
      "movq %%r9, %q4\n"
      /* (r10,r8) += n3 */
      "addq %%r14, %%r10\n"
      "adcq $0, %%r8\n"
      /* extract m5 */
      "movq %%r10, %q5\n"
      /* extract m6 */
      "movq %%r8, %q6\n"
      : "=g"(m0), "=g"(m1), "=g"(m2), "=g"(m3), "=g"(m4), "=g"(m5), "=g"(m6)
      : "S"(l), "i"(SECP256K1_N_C_0), "i"(SECP256K1_N_C_1)
      : "rax", "rdx", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "cc");
  
      /* Reduce 385 bits into 258. */
      __asm__ __volatile__(
      /* Preload */
      "movq %q9, %%r11\n"
      "movq %q10, %%r12\n"
      "movq %q11, %%r13\n"
      /* Initialize (r8,r9,r10) */
      "movq %q5, %%r8\n"
      "xorq %%r9, %%r9\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9) += m4 * c0 */
      "movq %12, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      /* extract p0 */
      "movq %%r8, %q0\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10) += m1 */
      "addq %q6, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r9,r10,r8) += m5 * c0 */
      "movq %12, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += m4 * c1 */
      "movq %13, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* extract p1 */
      "movq %%r9, %q1\n"
      "xorq %%r9, %%r9\n"
      /* (r10,r8,r9) += m2 */
      "addq %q7, %%r10\n"
      "adcq $0, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += m6 * c0 */
      "movq %12, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += m5 * c1 */
      "movq %13, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += m4 */
      "addq %%r11, %%r10\n"
      "adcq $0, %%r8\n"
      "adcq $0, %%r9\n"
      /* extract p2 */
      "movq %%r10, %q2\n"
      /* (r8,r9) += m3 */
      "addq %q8, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r8,r9) += m6 * c1 */
      "movq %13, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      /* (r8,r9) += m5 */
      "addq %%r12, %%r8\n"
      "adcq $0, %%r9\n"
      /* extract p3 */
      "movq %%r8, %q3\n"
      /* (r9) += m6 */
      "addq %%r13, %%r9\n"
      /* extract p4 */
      "movq %%r9, %q4\n"
      : "=&g"(p0), "=&g"(p1), "=&g"(p2), "=g"(p3), "=g"(p4)
      : "g"(m0), "g"(m1), "g"(m2), "g"(m3), "g"(m4), "g"(m5), "g"(m6), "i"(SECP256K1_N_C_0), "i"(SECP256K1_N_C_1)
      : "rax", "rdx", "r8", "r9", "r10", "r11", "r12", "r13", "cc");
  
      /* Reduce 258 bits into 256. */
      __asm__ __volatile__(
      /* Preload */
      "movq %q5, %%r10\n"
      /* (rax,rdx) = p4 * c0 */
      "movq %7, %%rax\n"
      "mulq %%r10\n"
      /* (rax,rdx) += p0 */
      "addq %q1, %%rax\n"
      "adcq $0, %%rdx\n"
      /* extract r0 */
      "movq %%rax, 0(%q6)\n"
      /* Move to (r8,r9) */
      "movq %%rdx, %%r8\n"
      "xorq %%r9, %%r9\n"
      /* (r8,r9) += p1 */
      "addq %q2, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r8,r9) += p4 * c1 */
      "movq %8, %%rax\n"
      "mulq %%r10\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      /* Extract r1 */
      "movq %%r8, 8(%q6)\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r8) += p4 */
      "addq %%r10, %%r9\n"
      "adcq $0, %%r8\n"
      /* (r9,r8) += p2 */
      "addq %q3, %%r9\n"
      "adcq $0, %%r8\n"
      /* Extract r2 */
      "movq %%r9, 16(%q6)\n"
      "xorq %%r9, %%r9\n"
      /* (r8,r9) += p3 */
      "addq %q4, %%r8\n"
      "adcq $0, %%r9\n"
      /* Extract r3 */
      "movq %%r8, 24(%q6)\n"
      /* Extract c */
      "movq %%r9, %q0\n"
      : "=g"(c)
      : "g"(p0), "g"(p1), "g"(p2), "g"(p3), "g"(p4), "D"(r), "i"(SECP256K1_N_C_0), "i"(SECP256K1_N_C_1)
      : "rax", "rdx", "r8", "r9", "r10", "cc", "memory");
  #else
      uint128_t c;
      uint64_t c0, c1, c2;
      uint64_t n0 = l[4], n1 = l[5], n2 = l[6], n3 = l[7];
      uint64_t m0, m1, m2, m3, m4, m5;
      uint32_t m6;
      uint64_t p0, p1, p2, p3;
      uint32_t p4;
  
      /* Reduce 512 bits into 385. */
      /* m[0..6] = l[0..3] + n[0..3] * SECP256K1_N_C. */
      c0 = l[0]; c1 = 0; c2 = 0;
      muladd_fast(n0, SECP256K1_N_C_0);
      extract_fast(m0);
      sumadd_fast(l[1]);
      muladd(n1, SECP256K1_N_C_0);
      muladd(n0, SECP256K1_N_C_1);
      extract(m1);
      sumadd(l[2]);
      muladd(n2, SECP256K1_N_C_0);
      muladd(n1, SECP256K1_N_C_1);
      sumadd(n0);
      extract(m2);
      sumadd(l[3]);
      muladd(n3, SECP256K1_N_C_0);
      muladd(n2, SECP256K1_N_C_1);
      sumadd(n1);
      extract(m3);
      muladd(n3, SECP256K1_N_C_1);
      sumadd(n2);
      extract(m4);
      sumadd_fast(n3);
      extract_fast(m5);
      VERIFY_CHECK(c0 <= 1);
      m6 = c0;
  
      /* Reduce 385 bits into 258. */
      /* p[0..4] = m[0..3] + m[4..6] * SECP256K1_N_C. */
      c0 = m0; c1 = 0; c2 = 0;
      muladd_fast(m4, SECP256K1_N_C_0);
      extract_fast(p0);
      sumadd_fast(m1);
      muladd(m5, SECP256K1_N_C_0);
      muladd(m4, SECP256K1_N_C_1);
      extract(p1);
      sumadd(m2);
      muladd(m6, SECP256K1_N_C_0);
      muladd(m5, SECP256K1_N_C_1);
      sumadd(m4);
      extract(p2);
      sumadd_fast(m3);
      muladd_fast(m6, SECP256K1_N_C_1);
      sumadd_fast(m5);
      extract_fast(p3);
      p4 = c0 + m6;
      VERIFY_CHECK(p4 <= 2);
  
      /* Reduce 258 bits into 256. */
      /* r[0..3] = p[0..3] + p[4] * SECP256K1_N_C. */
      c = p0 + (uint128_t)SECP256K1_N_C_0 * p4;
      r->d[0] = c & 0xFFFFFFFFFFFFFFFFULL; c >>= 64;
      c += p1 + (uint128_t)SECP256K1_N_C_1 * p4;
      r->d[1] = c & 0xFFFFFFFFFFFFFFFFULL; c >>= 64;
      c += p2 + (uint128_t)p4;
      r->d[2] = c & 0xFFFFFFFFFFFFFFFFULL; c >>= 64;
      c += p3;
      r->d[3] = c & 0xFFFFFFFFFFFFFFFFULL; c >>= 64;
  #endif
  
      /* Final reduction of r. */
      rustsecp256k1zkp_v0_2_0_scalar_reduce(r, c + rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r));
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_mul_512(uint64_t l[8], const rustsecp256k1zkp_v0_2_0_scalar *a, const rustsecp256k1zkp_v0_2_0_scalar *b) {
  #ifdef USE_ASM_X86_64
      const uint64_t *pb = b->d;
      __asm__ __volatile__(
      /* Preload */
      "movq 0(%%rdi), %%r15\n"
      "movq 8(%%rdi), %%rbx\n"
      "movq 16(%%rdi), %%rcx\n"
      "movq 0(%%rdx), %%r11\n"
      "movq 8(%%rdx), %%r12\n"
      "movq 16(%%rdx), %%r13\n"
      "movq 24(%%rdx), %%r14\n"
      /* (rax,rdx) = a0 * b0 */
      "movq %%r15, %%rax\n"
      "mulq %%r11\n"
      /* Extract l0 */
      "movq %%rax, 0(%%rsi)\n"
      /* (r8,r9,r10) = (rdx) */
      "movq %%rdx, %%r8\n"
      "xorq %%r9, %%r9\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9,r10) += a0 * b1 */
      "movq %%r15, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += a1 * b0 */
      "movq %%rbx, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* Extract l1 */
      "movq %%r8, 8(%%rsi)\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10,r8) += a0 * b2 */
      "movq %%r15, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += a1 * b1 */
      "movq %%rbx, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += a2 * b0 */
      "movq %%rcx, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* Extract l2 */
      "movq %%r9, 16(%%rsi)\n"
      "xorq %%r9, %%r9\n"
      /* (r10,r8,r9) += a0 * b3 */
      "movq %%r15, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* Preload a3 */
      "movq 24(%%rdi), %%r15\n"
      /* (r10,r8,r9) += a1 * b2 */
      "movq %%rbx, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += a2 * b1 */
      "movq %%rcx, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += a3 * b0 */
      "movq %%r15, %%rax\n"
      "mulq %%r11\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* Extract l3 */
      "movq %%r10, 24(%%rsi)\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9,r10) += a1 * b3 */
      "movq %%rbx, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += a2 * b2 */
      "movq %%rcx, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += a3 * b1 */
      "movq %%r15, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* Extract l4 */
      "movq %%r8, 32(%%rsi)\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10,r8) += a2 * b3 */
      "movq %%rcx, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += a3 * b2 */
      "movq %%r15, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* Extract l5 */
      "movq %%r9, 40(%%rsi)\n"
      /* (r10,r8) += a3 * b3 */
      "movq %%r15, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      /* Extract l6 */
      "movq %%r10, 48(%%rsi)\n"
      /* Extract l7 */
      "movq %%r8, 56(%%rsi)\n"
      : "+d"(pb)
      : "S"(l), "D"(a->d)
      : "rax", "rbx", "rcx", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15", "cc", "memory");
  #else
      /* 160 bit accumulator. */
      uint64_t c0 = 0, c1 = 0;
      uint32_t c2 = 0;
  
      /* l[0..7] = a[0..3] * b[0..3]. */
      muladd_fast(a->d[0], b->d[0]);
      extract_fast(l[0]);
      muladd(a->d[0], b->d[1]);
      muladd(a->d[1], b->d[0]);
      extract(l[1]);
      muladd(a->d[0], b->d[2]);
      muladd(a->d[1], b->d[1]);
      muladd(a->d[2], b->d[0]);
      extract(l[2]);
      muladd(a->d[0], b->d[3]);
      muladd(a->d[1], b->d[2]);
      muladd(a->d[2], b->d[1]);
      muladd(a->d[3], b->d[0]);
      extract(l[3]);
      muladd(a->d[1], b->d[3]);
      muladd(a->d[2], b->d[2]);
      muladd(a->d[3], b->d[1]);
      extract(l[4]);
      muladd(a->d[2], b->d[3]);
      muladd(a->d[3], b->d[2]);
      extract(l[5]);
      muladd_fast(a->d[3], b->d[3]);
      extract_fast(l[6]);
      VERIFY_CHECK(c1 == 0);
      l[7] = c0;
  #endif
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_sqr_512(uint64_t l[8], const rustsecp256k1zkp_v0_2_0_scalar *a) {
  #ifdef USE_ASM_X86_64
      __asm__ __volatile__(
      /* Preload */
      "movq 0(%%rdi), %%r11\n"
      "movq 8(%%rdi), %%r12\n"
      "movq 16(%%rdi), %%r13\n"
      "movq 24(%%rdi), %%r14\n"
      /* (rax,rdx) = a0 * a0 */
      "movq %%r11, %%rax\n"
      "mulq %%r11\n"
      /* Extract l0 */
      "movq %%rax, 0(%%rsi)\n"
      /* (r8,r9,r10) = (rdx,0) */
      "movq %%rdx, %%r8\n"
      "xorq %%r9, %%r9\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9,r10) += 2 * a0 * a1 */
      "movq %%r11, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* Extract l1 */
      "movq %%r8, 8(%%rsi)\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10,r8) += 2 * a0 * a2 */
      "movq %%r11, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* (r9,r10,r8) += a1 * a1 */
      "movq %%r12, %%rax\n"
      "mulq %%r12\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* Extract l2 */
      "movq %%r9, 16(%%rsi)\n"
      "xorq %%r9, %%r9\n"
      /* (r10,r8,r9) += 2 * a0 * a3 */
      "movq %%r11, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* (r10,r8,r9) += 2 * a1 * a2 */
      "movq %%r12, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      "adcq $0, %%r9\n"
      /* Extract l3 */
      "movq %%r10, 24(%%rsi)\n"
      "xorq %%r10, %%r10\n"
      /* (r8,r9,r10) += 2 * a1 * a3 */
      "movq %%r12, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* (r8,r9,r10) += a2 * a2 */
      "movq %%r13, %%rax\n"
      "mulq %%r13\n"
      "addq %%rax, %%r8\n"
      "adcq %%rdx, %%r9\n"
      "adcq $0, %%r10\n"
      /* Extract l4 */
      "movq %%r8, 32(%%rsi)\n"
      "xorq %%r8, %%r8\n"
      /* (r9,r10,r8) += 2 * a2 * a3 */
      "movq %%r13, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      "addq %%rax, %%r9\n"
      "adcq %%rdx, %%r10\n"
      "adcq $0, %%r8\n"
      /* Extract l5 */
      "movq %%r9, 40(%%rsi)\n"
      /* (r10,r8) += a3 * a3 */
      "movq %%r14, %%rax\n"
      "mulq %%r14\n"
      "addq %%rax, %%r10\n"
      "adcq %%rdx, %%r8\n"
      /* Extract l6 */
      "movq %%r10, 48(%%rsi)\n"
      /* Extract l7 */
      "movq %%r8, 56(%%rsi)\n"
      :
      : "S"(l), "D"(a->d)
      : "rax", "rdx", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "cc", "memory");
  #else
      /* 160 bit accumulator. */
      uint64_t c0 = 0, c1 = 0;
      uint32_t c2 = 0;
  
      /* l[0..7] = a[0..3] * b[0..3]. */
      muladd_fast(a->d[0], a->d[0]);
      extract_fast(l[0]);
      muladd2(a->d[0], a->d[1]);
      extract(l[1]);
      muladd2(a->d[0], a->d[2]);
      muladd(a->d[1], a->d[1]);
      extract(l[2]);
      muladd2(a->d[0], a->d[3]);
      muladd2(a->d[1], a->d[2]);
      extract(l[3]);
      muladd2(a->d[1], a->d[3]);
      muladd(a->d[2], a->d[2]);
      extract(l[4]);
      muladd2(a->d[2], a->d[3]);
      extract(l[5]);
      muladd_fast(a->d[3], a->d[3]);
      extract_fast(l[6]);
      VERIFY_CHECK(c1 == 0);
      l[7] = c0;
  #endif
  }
  
  #undef sumadd
  #undef sumadd_fast
  #undef muladd
  #undef muladd_fast
  #undef muladd2
  #undef extract
  #undef extract_fast
  
  static void rustsecp256k1zkp_v0_2_0_scalar_mul(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a, const rustsecp256k1zkp_v0_2_0_scalar *b) {
      uint64_t l[8];
      rustsecp256k1zkp_v0_2_0_scalar_mul_512(l, a, b);
      rustsecp256k1zkp_v0_2_0_scalar_reduce_512(r, l);
  }
  
  static int rustsecp256k1zkp_v0_2_0_scalar_shr_int(rustsecp256k1zkp_v0_2_0_scalar *r, int n) {
      int ret;
      VERIFY_CHECK(n > 0);
      VERIFY_CHECK(n < 16);
      ret = r->d[0] & ((1 << n) - 1);
      r->d[0] = (r->d[0] >> n) + (r->d[1] << (64 - n));
      r->d[1] = (r->d[1] >> n) + (r->d[2] << (64 - n));
      r->d[2] = (r->d[2] >> n) + (r->d[3] << (64 - n));
      r->d[3] = (r->d[3] >> n);
      return ret;
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_sqr(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a) {
      uint64_t l[8];
      rustsecp256k1zkp_v0_2_0_scalar_sqr_512(l, a);
      rustsecp256k1zkp_v0_2_0_scalar_reduce_512(r, l);
  }
  
  static void rustsecp256k1zkp_v0_2_0_scalar_split_128(rustsecp256k1zkp_v0_2_0_scalar *r1, rustsecp256k1zkp_v0_2_0_scalar *r2, const rustsecp256k1zkp_v0_2_0_scalar *k) {
      r1->d[0] = k->d[0];
      r1->d[1] = k->d[1];
      r1->d[2] = 0;
      r1->d[3] = 0;
      r2->d[0] = k->d[2];
      r2->d[1] = k->d[3];
      r2->d[2] = 0;
      r2->d[3] = 0;
  }
  
  SECP256K1_INLINE static int rustsecp256k1zkp_v0_2_0_scalar_eq(const rustsecp256k1zkp_v0_2_0_scalar *a, const rustsecp256k1zkp_v0_2_0_scalar *b) {
      return ((a->d[0] ^ b->d[0]) | (a->d[1] ^ b->d[1]) | (a->d[2] ^ b->d[2]) | (a->d[3] ^ b->d[3])) == 0;
  }
  
  SECP256K1_INLINE static void rustsecp256k1zkp_v0_2_0_scalar_mul_shift_var(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a, const rustsecp256k1zkp_v0_2_0_scalar *b, unsigned int shift) {
      uint64_t l[8];
      unsigned int shiftlimbs;
      unsigned int shiftlow;
      unsigned int shifthigh;
      VERIFY_CHECK(shift >= 256);
      rustsecp256k1zkp_v0_2_0_scalar_mul_512(l, a, b);
      shiftlimbs = shift >> 6;
      shiftlow = shift & 0x3F;
      shifthigh = 64 - shiftlow;
      r->d[0] = shift < 512 ? (l[0 + shiftlimbs] >> shiftlow | (shift < 448 && shiftlow ? (l[1 + shiftlimbs] << shifthigh) : 0)) : 0;
      r->d[1] = shift < 448 ? (l[1 + shiftlimbs] >> shiftlow | (shift < 384 && shiftlow ? (l[2 + shiftlimbs] << shifthigh) : 0)) : 0;
      r->d[2] = shift < 384 ? (l[2 + shiftlimbs] >> shiftlow | (shift < 320 && shiftlow ? (l[3 + shiftlimbs] << shifthigh) : 0)) : 0;
      r->d[3] = shift < 320 ? (l[3 + shiftlimbs] >> shiftlow) : 0;
      rustsecp256k1zkp_v0_2_0_scalar_cadd_bit(r, 0, (l[(shift - 1) >> 6] >> ((shift - 1) & 0x3f)) & 1);
  }
  
  static SECP256K1_INLINE void rustsecp256k1zkp_v0_2_0_scalar_cmov(rustsecp256k1zkp_v0_2_0_scalar *r, const rustsecp256k1zkp_v0_2_0_scalar *a, int flag) {
      uint64_t mask0, mask1;
      VG_CHECK_VERIFY(r->d, sizeof(r->d));
      mask0 = flag + ~((uint64_t)0);
      mask1 = ~mask0;
      r->d[0] = (r->d[0] & mask0) | (a->d[0] & mask1);
      r->d[1] = (r->d[1] & mask0) | (a->d[1] & mask1);
      r->d[2] = (r->d[2] & mask0) | (a->d[2] & mask1);
      r->d[3] = (r->d[3] & mask0) | (a->d[3] & mask1);
  }
  
  #define ROTL32(x,n) ((x) << (n) | (x) >> (32-(n)))
  #define QUARTERROUND(a,b,c,d) \
    a += b; d = ROTL32(d ^ a, 16); \
    c += d; b = ROTL32(b ^ c, 12); \
    a += b; d = ROTL32(d ^ a, 8); \
    c += d; b = ROTL32(b ^ c, 7);
  
  #if defined(SECP256K1_BIG_ENDIAN)
  #define LE32(p) ((((p) & 0xFF) << 24) | (((p) & 0xFF00) << 8) | (((p) & 0xFF0000) >> 8) | (((p) & 0xFF000000) >> 24))
  #elif defined(SECP256K1_LITTLE_ENDIAN)
  #define LE32(p) (p)
  #endif
  
  static void rustsecp256k1zkp_v0_2_0_scalar_chacha20(rustsecp256k1zkp_v0_2_0_scalar *r1, rustsecp256k1zkp_v0_2_0_scalar *r2, const unsigned char *seed, uint64_t idx) {
      size_t n;
      size_t over_count = 0;
      uint32_t seed32[8];
      uint32_t x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
      int over1, over2;
  
      memcpy((void *) seed32, (const void *) seed, 32);
      do {
          x0 = 0x61707865;
          x1 = 0x3320646e;
          x2 = 0x79622d32;
          x3 = 0x6b206574;
          x4 = LE32(seed32[0]);
          x5 = LE32(seed32[1]);
          x6 = LE32(seed32[2]);
          x7 = LE32(seed32[3]);
          x8 = LE32(seed32[4]);
          x9 = LE32(seed32[5]);
          x10 = LE32(seed32[6]);
          x11 = LE32(seed32[7]);
          x12 = idx;
          x13 = idx >> 32;
          x14 = 0;
          x15 = over_count;
  
          n = 10;
          while (n--) {
              QUARTERROUND(x0, x4, x8,x12)
              QUARTERROUND(x1, x5, x9,x13)
              QUARTERROUND(x2, x6,x10,x14)
              QUARTERROUND(x3, x7,x11,x15)
              QUARTERROUND(x0, x5,x10,x15)
              QUARTERROUND(x1, x6,x11,x12)
              QUARTERROUND(x2, x7, x8,x13)
              QUARTERROUND(x3, x4, x9,x14)
          }
  
          x0 += 0x61707865;
          x1 += 0x3320646e;
          x2 += 0x79622d32;
          x3 += 0x6b206574;
          x4 += LE32(seed32[0]);
          x5 += LE32(seed32[1]);
          x6 += LE32(seed32[2]);
          x7 += LE32(seed32[3]);
          x8 += LE32(seed32[4]);
          x9 += LE32(seed32[5]);
          x10 += LE32(seed32[6]);
          x11 += LE32(seed32[7]);
          x12 += idx;
          x13 += idx >> 32;
          x14 += 0;
          x15 += over_count;
  
          r1->d[3] = (((uint64_t)  x0) << 32) | x1;
          r1->d[2] = (((uint64_t)  x2) << 32) | x3;
          r1->d[1] = (((uint64_t)  x4) << 32) | x5;
          r1->d[0] = (((uint64_t)  x6) << 32) | x7;
          r2->d[3] = (((uint64_t)  x8) << 32) | x9;
          r2->d[2] = (((uint64_t) x10) << 32) | x11;
          r2->d[1] = (((uint64_t) x12) << 32) | x13;
          r2->d[0] = (((uint64_t) x14) << 32) | x15;
  
          over1 = rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r1);
          over2 = rustsecp256k1zkp_v0_2_0_scalar_check_overflow(r2);
          over_count++;
     } while (over1 | over2);
  }
  
  #undef ROTL32
  #undef QUARTERROUND
  #undef LE32
  
  #endif /* SECP256K1_SCALAR_REPR_IMPL_H */
  