text: /*
  	poly1305 implementation using 32 bit * 32 bit = 64 bit multiplication and 64 bit addition
  */
  
  #if defined(_MSC_VER)
  	#define POLY1305_NOINLINE __declspec(noinline)
  #elif defined(__GNUC__)
  	#define POLY1305_NOINLINE __attribute__((noinline))
  #else
  	#define POLY1305_NOINLINE
  #endif
  
  #define poly1305_block_size 16
  
  /* 17 + sizeof(size_t) + 14*sizeof(unsigned long) */
  typedef struct poly1305_state_internal_t {
  	unsigned long r[5];
  	unsigned long h[5];
  	unsigned long pad[4];
  	size_t leftover;
  	unsigned char buffer[poly1305_block_size];
  	unsigned char final;
  } poly1305_state_internal_t;
  
  /* interpret four 8 bit unsigned integers as a 32 bit unsigned integer in little endian */
  static unsigned long
  U8TO32(const unsigned char *p) {
  	return
  		(((unsigned long)(p[0] & 0xff)      ) |
  	     ((unsigned long)(p[1] & 0xff) <<  8) |
           ((unsigned long)(p[2] & 0xff) << 16) |
           ((unsigned long)(p[3] & 0xff) << 24));
  }
  
  /* store a 32 bit unsigned integer as four 8 bit unsigned integers in little endian */
  static void
  U32TO8(unsigned char *p, unsigned long v) {
  	p[0] = (v      ) & 0xff;
  	p[1] = (v >>  8) & 0xff;
  	p[2] = (v >> 16) & 0xff;
  	p[3] = (v >> 24) & 0xff;
  }
  
  void
  poly1305_init(poly1305_context *ctx, unsigned char *key) {
  	poly1305_state_internal_t *st = (poly1305_state_internal_t *)ctx;
  
  	/* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
  	st->r[0] = (U8TO32(&key[ 0])     ) & 0x3ffffff;
  	st->r[1] = (U8TO32(&key[ 3]) >> 2) & 0x3ffff03;
  	st->r[2] = (U8TO32(&key[ 6]) >> 4) & 0x3ffc0ff;
  	st->r[3] = (U8TO32(&key[ 9]) >> 6) & 0x3f03fff;
  	st->r[4] = (U8TO32(&key[12]) >> 8) & 0x00fffff;
  
  	/* h = 0 */
  	st->h[0] = 0;
  	st->h[1] = 0;
  	st->h[2] = 0;
  	st->h[3] = 0;
  	st->h[4] = 0;
  
  	/* save pad for later */
  	st->pad[0] = U8TO32(&key[16]);
  	st->pad[1] = U8TO32(&key[20]);
  	st->pad[2] = U8TO32(&key[24]);
  	st->pad[3] = U8TO32(&key[28]);
  
  	st->leftover = 0;
  	st->final = 0;
  }
  
  static void
  poly1305_blocks(poly1305_state_internal_t *st, const unsigned char *m, size_t bytes) {
  	const unsigned long hibit = (st->final) ? 0 : (1 << 24); /* 1 << 128 */
  	unsigned long r0,r1,r2,r3,r4;
  	unsigned long s1,s2,s3,s4;
  	unsigned long h0,h1,h2,h3,h4;
  	unsigned long long d0,d1,d2,d3,d4;
  	unsigned long c;
  
  	r0 = st->r[0];
  	r1 = st->r[1];
  	r2 = st->r[2];
  	r3 = st->r[3];
  	r4 = st->r[4];
  
  	s1 = r1 * 5;
  	s2 = r2 * 5;
  	s3 = r3 * 5;
  	s4 = r4 * 5;
  
  	h0 = st->h[0];
  	h1 = st->h[1];
  	h2 = st->h[2];
  	h3 = st->h[3];
  	h4 = st->h[4];
  
  	while (bytes >= poly1305_block_size) {
  		/* h += m[i] */
  		h0 += (U8TO32(m+ 0)     ) & 0x3ffffff;
  		h1 += (U8TO32(m+ 3) >> 2) & 0x3ffffff;
  		h2 += (U8TO32(m+ 6) >> 4) & 0x3ffffff;
  		h3 += (U8TO32(m+ 9) >> 6) & 0x3ffffff;
  		h4 += (U8TO32(m+12) >> 8) | hibit;
  
  		/* h *= r */
  		d0 = ((unsigned long long)h0 * r0) + ((unsigned long long)h1 * s4) + ((unsigned long long)h2 * s3) + ((unsigned long long)h3 * s2) + ((unsigned long long)h4 * s1);
  		d1 = ((unsigned long long)h0 * r1) + ((unsigned long long)h1 * r0) + ((unsigned long long)h2 * s4) + ((unsigned long long)h3 * s3) + ((unsigned long long)h4 * s2);
  		d2 = ((unsigned long long)h0 * r2) + ((unsigned long long)h1 * r1) + ((unsigned long long)h2 * r0) + ((unsigned long long)h3 * s4) + ((unsigned long long)h4 * s3);
  		d3 = ((unsigned long long)h0 * r3) + ((unsigned long long)h1 * r2) + ((unsigned long long)h2 * r1) + ((unsigned long long)h3 * r0) + ((unsigned long long)h4 * s4);
  		d4 = ((unsigned long long)h0 * r4) + ((unsigned long long)h1 * r3) + ((unsigned long long)h2 * r2) + ((unsigned long long)h3 * r1) + ((unsigned long long)h4 * r0);
  
  		/* (partial) h %= p */
  		              c = (unsigned long)(d0 >> 26); h0 = (unsigned long)d0 & 0x3ffffff;
  		d1 += c;      c = (unsigned long)(d1 >> 26); h1 = (unsigned long)d1 & 0x3ffffff;
  		d2 += c;      c = (unsigned long)(d2 >> 26); h2 = (unsigned long)d2 & 0x3ffffff;
  		d3 += c;      c = (unsigned long)(d3 >> 26); h3 = (unsigned long)d3 & 0x3ffffff;
  		d4 += c;      c = (unsigned long)(d4 >> 26); h4 = (unsigned long)d4 & 0x3ffffff;
  		h0 += c * 5;  c =                (h0 >> 26); h0 =                h0 & 0x3ffffff;
  		h1 += c;
  
  		m += poly1305_block_size;
  		bytes -= poly1305_block_size;
  	}
  
  	st->h[0] = h0;
  	st->h[1] = h1;
  	st->h[2] = h2;
  	st->h[3] = h3;
  	st->h[4] = h4;
  }
  
  POLY1305_NOINLINE void
  poly1305_finish(poly1305_context *ctx, unsigned char *mac) {
  	poly1305_state_internal_t *st = (poly1305_state_internal_t *)ctx;
  	unsigned long h0,h1,h2,h3,h4,c;
  	unsigned long g0,g1,g2,g3,g4;
  	unsigned long long f;
  	unsigned long mask;
  
  	/* process the remaining block */
  	if (st->leftover) {
  		size_t i = st->leftover;
  		st->buffer[i++] = 1;
  		for (; i < poly1305_block_size; i++)
  			st->buffer[i] = 0;
  		st->final = 1;
  		poly1305_blocks(st, st->buffer, poly1305_block_size);
  	}
  
  	/* fully carry h */
  	h0 = st->h[0];
  	h1 = st->h[1];
  	h2 = st->h[2];
  	h3 = st->h[3];
  	h4 = st->h[4];
  
  	             c = h1 >> 26; h1 = h1 & 0x3ffffff;
  	h2 +=     c; c = h2 >> 26; h2 = h2 & 0x3ffffff;
  	h3 +=     c; c = h3 >> 26; h3 = h3 & 0x3ffffff;
  	h4 +=     c; c = h4 >> 26; h4 = h4 & 0x3ffffff;
  	h0 += c * 5; c = h0 >> 26; h0 = h0 & 0x3ffffff;
  	h1 +=     c;
  
  	/* compute h + -p */
  	g0 = h0 + 5; c = g0 >> 26; g0 &= 0x3ffffff;
  	g1 = h1 + c; c = g1 >> 26; g1 &= 0x3ffffff;
  	g2 = h2 + c; c = g2 >> 26; g2 &= 0x3ffffff;
  	g3 = h3 + c; c = g3 >> 26; g3 &= 0x3ffffff;
  	g4 = h4 + c - (1 << 26);
  
  	/* select h if h < p, or h + -p if h >= p */
  	mask = (g4 >> ((sizeof(unsigned long) * 8) - 1)) - 1;
  	g0 &= mask;
  	g1 &= mask;
  	g2 &= mask;
  	g3 &= mask;
  	g4 &= mask;
  	mask = ~mask;
  	h0 = (h0 & mask) | g0;
  	h1 = (h1 & mask) | g1;
  	h2 = (h2 & mask) | g2;
  	h3 = (h3 & mask) | g3;
  	h4 = (h4 & mask) | g4;
  
  	/* h = h % (2^128) */
  	h0 = ((h0      ) | (h1 << 26)) & 0xffffffff;
  	h1 = ((h1 >>  6) | (h2 << 20)) & 0xffffffff;
  	h2 = ((h2 >> 12) | (h3 << 14)) & 0xffffffff;
  	h3 = ((h3 >> 18) | (h4 <<  8)) & 0xffffffff;
  
  	/* mac = (h + pad) % (2^128) */
  	f = (unsigned long long)h0 + st->pad[0]            ; h0 = (unsigned long)f;
  	f = (unsigned long long)h1 + st->pad[1] + (f >> 32); h1 = (unsigned long)f;
  	f = (unsigned long long)h2 + st->pad[2] + (f >> 32); h2 = (unsigned long)f;
  	f = (unsigned long long)h3 + st->pad[3] + (f >> 32); h3 = (unsigned long)f;
  
  	U32TO8(mac +  0, h0);
  	U32TO8(mac +  4, h1);
  	U32TO8(mac +  8, h2);
  	U32TO8(mac + 12, h3);
  
  	/* zero out the state */
  	st->h[0] = 0;
  	st->h[1] = 0;
  	st->h[2] = 0;
  	st->h[3] = 0;
  	st->h[4] = 0;
  	st->r[0] = 0;
  	st->r[1] = 0;
  	st->r[2] = 0;
  	st->r[3] = 0;
  	st->r[4] = 0;
  	st->pad[0] = 0;
  	st->pad[1] = 0;
  	st->pad[2] = 0;
  	st->pad[3] = 0;
  }
  
  