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/* See LICENSE file for copyright and license details. */
#include "common.h"
static void
encode_uint64_le(unsigned char *out, uint_least64_t value, size_t bytes)
{
/* Adding LIKELY to indicate that the default case is the
* expected does not affact the output */
switch (bytes) {
default:
/*
* The following optimisation have been tested:
*
* 1) Changing the default case, on amd64, to
* *(uint64_t *)out = (uint64_t)value;
* break;
* result: halved performance
*/
out[7] = (unsigned char)((value >> 56) & 255);
/* fall through */
case 7:
out[6] = (unsigned char)((value >> 48) & 255);
/* fall through */
case 6:
out[5] = (unsigned char)((value >> 40) & 255);
/* fall through */
case 5:
out[4] = (unsigned char)((value >> 32) & 255);
/* fall through */
case 4:
out[3] = (unsigned char)((value >> 24) & 255);
/* fall through */
case 3:
out[2] = (unsigned char)((value >> 16) & 255);
/* fall through */
case 2:
out[1] = (unsigned char)((value >> 8) & 255);
/* fall through */
case 1:
out[0] = (unsigned char)((value >> 0) & 255);
/* fall through */
case 0:
break;
}
}
void
libblake_internal_blake2b_output_digest(struct libblake_blake2b_state *state, size_t output_len, unsigned char *output)
{
size_t i, j;
#ifdef LITTLE_ENDIAN
if ((uint_least64_t)(UINT_LEAST64_C(0xFFFFffffFFFFffff) + 1) == 0) {
/* 37.5x performance improvement;
* even though the compiler is smart enough to optimise
* `encode_uint64_le(&output[i], state->h[j], 8);` to a
* movq (on amd64), it is note smart enough to optimise
* the rest */
memcpy(output, state->h, output_len);
return;
}
#endif
/* Estimated to have similar performance benefit as above
* on big-endian machines */
for (i = 0, j = 0; i + 8 < output_len; i += 8, j += 1)
encode_uint64_le(&output[i], state->h[j], 8);
encode_uint64_le(&output[i], state->h[j], output_len - i);
/*
* Unoptimised code:
*
* for (i = 0, j = 0; i < output_len; i += 8, j += 1)
* encode_uint64_le(&output[i], state->h[j], output_len - i);
*/
}
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