text: /*
   * Copyright 2014-2021 The OpenSSL Project Authors. All Rights Reserved.
   *
   * Licensed under the Apache License 2.0 (the "License").  You may not use
   * this file except in compliance with the License.  You can obtain a copy
   * in the file LICENSE in the source distribution or at
   * https://www.openssl.org/source/license.html
   */
  
  #ifndef OSSL_INTERNAL_CONSTANT_TIME_H
  # define OSSL_INTERNAL_CONSTANT_TIME_H
  # if defined(__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ > 3))
  # pragma once
  # endif
  
  # include <stdlib.h>
  # include <string.h>
  # include <openssl/e_os2.h>              /* For 'ossl_inline' */
  
  /*-
   * The boolean methods return a bitmask of all ones (0xff...f) for true
   * and 0 for false. This is useful for choosing a value based on the result
   * of a conditional in constant time. For example,
   *      if (a < b) {
   *        c = a;
   *      } else {
   *        c = b;
   *      }
   * can be written as
   *      unsigned int lt = constant_time_lt(a, b);
   *      c = constant_time_select(lt, a, b);
   */
  
  /* Returns the given value with the MSB copied to all the other bits. */
  static ossl_inline unsigned int constant_time_msb(unsigned int a);
  /* Convenience method for uint32_t. */
  static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
  /* Convenience method for uint64_t. */
  static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
  
  /* Returns 0xff..f if a < b and 0 otherwise. */
  static ossl_inline unsigned int constant_time_lt(unsigned int a,
                                                   unsigned int b);
  /* Convenience method for getting an 8-bit mask. */
  static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
                                                      unsigned int b);
  /* Convenience method for uint64_t. */
  static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b);
  
  /* Returns 0xff..f if a >= b and 0 otherwise. */
  static ossl_inline unsigned int constant_time_ge(unsigned int a,
                                                   unsigned int b);
  /* Convenience method for getting an 8-bit mask. */
  static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
                                                      unsigned int b);
  
  /* Returns 0xff..f if a == 0 and 0 otherwise. */
  static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
  /* Convenience method for getting an 8-bit mask. */
  static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
  /* Convenience method for getting a 32-bit mask. */
  static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a);
  
  /* Returns 0xff..f if a == b and 0 otherwise. */
  static ossl_inline unsigned int constant_time_eq(unsigned int a,
                                                   unsigned int b);
  /* Convenience method for getting an 8-bit mask. */
  static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
                                                      unsigned int b);
  /* Signed integers. */
  static ossl_inline unsigned int constant_time_eq_int(int a, int b);
  /* Convenience method for getting an 8-bit mask. */
  static ossl_inline unsigned char constant_time_eq_int_8(int a, int b);
  
  /*-
   * Returns (mask & a) | (~mask & b).
   *
   * When |mask| is all 1s or all 0s (as returned by the methods above),
   * the select methods return either |a| (if |mask| is nonzero) or |b|
   * (if |mask| is zero).
   */
  static ossl_inline unsigned int constant_time_select(unsigned int mask,
                                                       unsigned int a,
                                                       unsigned int b);
  /* Convenience method for unsigned chars. */
  static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
                                                          unsigned char a,
                                                          unsigned char b);
  
  /* Convenience method for uint32_t. */
  static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
                                                      uint32_t b);
  
  /* Convenience method for uint64_t. */
  static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
                                                      uint64_t b);
  /* Convenience method for signed integers. */
  static ossl_inline int constant_time_select_int(unsigned int mask, int a,
                                                  int b);
  
  
  static ossl_inline unsigned int constant_time_msb(unsigned int a)
  {
      return 0 - (a >> (sizeof(a) * 8 - 1));
  }
  
  
  static ossl_inline uint32_t constant_time_msb_32(uint32_t a)
  {
      return 0 - (a >> 31);
  }
  
  static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
  {
      return 0 - (a >> 63);
  }
  
  static ossl_inline size_t constant_time_msb_s(size_t a)
  {
      return 0 - (a >> (sizeof(a) * 8 - 1));
  }
  
  static ossl_inline unsigned int constant_time_lt(unsigned int a,
                                                   unsigned int b)
  {
      return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
  }
  
  static ossl_inline size_t constant_time_lt_s(size_t a, size_t b)
  {
      return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
  }
  
  static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
                                                      unsigned int b)
  {
      return (unsigned char)constant_time_lt(a, b);
  }
  
  static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b)
  {
      return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b)));
  }
  
  static ossl_inline unsigned int constant_time_ge(unsigned int a,
                                                   unsigned int b)
  {
      return ~constant_time_lt(a, b);
  }
  
  static ossl_inline size_t constant_time_ge_s(size_t a, size_t b)
  {
      return ~constant_time_lt_s(a, b);
  }
  
  static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
                                                      unsigned int b)
  {
      return (unsigned char)constant_time_ge(a, b);
  }
  
  static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
  {
      return (unsigned char)constant_time_ge_s(a, b);
  }
  
  static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
  {
      return constant_time_msb(~a & (a - 1));
  }
  
  static ossl_inline size_t constant_time_is_zero_s(size_t a)
  {
      return constant_time_msb_s(~a & (a - 1));
  }
  
  static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
  {
      return (unsigned char)constant_time_is_zero(a);
  }
  
  static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a)
  {
      return constant_time_msb_32(~a & (a - 1));
  }
  
  static ossl_inline uint64_t constant_time_is_zero_64(uint64_t a)
  {
      return constant_time_msb_64(~a & (a - 1));
  }
  
  static ossl_inline unsigned int constant_time_eq(unsigned int a,
                                                   unsigned int b)
  {
      return constant_time_is_zero(a ^ b);
  }
  
  static ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
  {
      return constant_time_is_zero_s(a ^ b);
  }
  
  static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
                                                      unsigned int b)
  {
      return (unsigned char)constant_time_eq(a, b);
  }
  
  static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
  {
      return (unsigned char)constant_time_eq_s(a, b);
  }
  
  static ossl_inline unsigned int constant_time_eq_int(int a, int b)
  {
      return constant_time_eq((unsigned)(a), (unsigned)(b));
  }
  
  static ossl_inline unsigned char constant_time_eq_int_8(int a, int b)
  {
      return constant_time_eq_8((unsigned)(a), (unsigned)(b));
  }
  
  /*
   * Returns the value unmodified, but avoids optimizations.
   * The barriers prevent the compiler from narrowing down the
   * possible value range of the mask and ~mask in the select
   * statements, which avoids the recognition of the select
   * and turning it into a conditional load or branch.
   */
  static ossl_inline unsigned int value_barrier(unsigned int a)
  {
  #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
      unsigned int r;
      __asm__("" : "=r"(r) : "0"(a));
  #else
      volatile unsigned int r = a;
  #endif
      return r;
  }
  
  /* Convenience method for uint32_t. */
  static ossl_inline uint32_t value_barrier_32(uint32_t a)
  {
  #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
      uint32_t r;
      __asm__("" : "=r"(r) : "0"(a));
  #else
      volatile uint32_t r = a;
  #endif
      return r;
  }
  
  /* Convenience method for uint64_t. */
  static ossl_inline uint64_t value_barrier_64(uint64_t a)
  {
  #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
      uint64_t r;
      __asm__("" : "=r"(r) : "0"(a));
  #else
      volatile uint64_t r = a;
  #endif
      return r;
  }
  
  /* Convenience method for size_t. */
  static ossl_inline size_t value_barrier_s(size_t a)
  {
  #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
      size_t r;
      __asm__("" : "=r"(r) : "0"(a));
  #else
      volatile size_t r = a;
  #endif
      return r;
  }
  
  static ossl_inline unsigned int constant_time_select(unsigned int mask,
                                                       unsigned int a,
                                                       unsigned int b)
  {
      return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
  }
  
  static ossl_inline size_t constant_time_select_s(size_t mask,
                                                   size_t a,
                                                   size_t b)
  {
      return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b);
  }
  
  static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
                                                          unsigned char a,
                                                          unsigned char b)
  {
      return (unsigned char)constant_time_select(mask, a, b);
  }
  
  static ossl_inline int constant_time_select_int(unsigned int mask, int a,
                                                  int b)
  {
      return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b));
  }
  
  static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
  {
      return (int)constant_time_select((unsigned)mask, (unsigned)(a),
                                        (unsigned)(b));
  }
  
  static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
                                                      uint32_t b)
  {
      return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b);
  }
  
  static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
                                                      uint64_t b)
  {
      return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b);
  }
  
  /*
   * mask must be 0xFFFFFFFF or 0x00000000.
   *
   * if (mask) {
   *     uint32_t tmp = *a;
   *
   *     *a = *b;
   *     *b = tmp;
   * }
   */
  static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
                                                     uint32_t *b)
  {
      uint32_t xor = *a ^ *b;
  
      xor &= mask;
      *a ^= xor;
      *b ^= xor;
  }
  
  /*
   * mask must be 0xFFFFFFFF or 0x00000000.
   *
   * if (mask) {
   *     uint64_t tmp = *a;
   *
   *     *a = *b;
   *     *b = tmp;
   * }
   */
  static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
                                                     uint64_t *b)
  {
      uint64_t xor = *a ^ *b;
  
      xor &= mask;
      *a ^= xor;
      *b ^= xor;
  }
  
  /*
   * mask must be 0xFF or 0x00.
   * "constant time" is per len.
   *
   * if (mask) {
   *     unsigned char tmp[len];
   *
   *     memcpy(tmp, a, len);
   *     memcpy(a, b);
   *     memcpy(b, tmp);
   * }
   */
  static ossl_inline void constant_time_cond_swap_buff(unsigned char mask,
                                                       unsigned char *a,
                                                       unsigned char *b,
                                                       size_t len)
  {
      size_t i;
      unsigned char tmp;
  
      for (i = 0; i < len; i++) {
          tmp = a[i] ^ b[i];
          tmp &= mask;
          a[i] ^= tmp;
          b[i] ^= tmp;
      }
  }
  
  /*
   * table is a two dimensional array of bytes. Each row has rowsize elements.
   * Copies row number idx into out. rowsize and numrows are not considered
   * private.
   */
  static ossl_inline void constant_time_lookup(void *out,
                                               const void *table,
                                               size_t rowsize,
                                               size_t numrows,
                                               size_t idx)
  {
      size_t i, j;
      const unsigned char *tablec = (const unsigned char *)table;
      unsigned char *outc = (unsigned char *)out;
      unsigned char mask;
  
      memset(out, 0, rowsize);
  
      /* Note idx may underflow - but that is well defined */
      for (i = 0; i < numrows; i++, idx--) {
          mask = (unsigned char)constant_time_is_zero_s(idx);
          for (j = 0; j < rowsize; j++)
              *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
      }
  }
  
  /*
   * Expected usage pattern is to unconditionally set error and then
   * wipe it if there was no actual error. |clear| is 1 or 0.
   */
  void err_clear_last_constant_time(int clear);
  
  #endif                          /* OSSL_INTERNAL_CONSTANT_TIME_H */
  