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Use __builtin_ctz to count trailing zeros

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
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Dave Rodgman
2023-08-09 18:56:07 +01:00
parent f3df105b37
commit fa703e38a2
1 changed files with 19 additions and 2 deletions
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21
library/bignum.c
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@ -330,16 +330,33 @@ cleanup:
*/
size_t mbedtls_mpi_lsb(const mbedtls_mpi *X)
{
size_t i, j, count = 0;
size_t i;
MBEDTLS_INTERNAL_VALIDATE_RET(X != NULL, 0);
#if defined(__has_builtin)
#if (MBEDTLS_MPI_UINT_MAX == UINT_MAX) && __has_builtin(__builtin_ctz)
#define mbedtls_mpi_uint_ctz __builtin_ctz
#elif (MBEDTLS_MPI_UINT_MAX == ULONG_MAX) && __has_builtin(__builtin_ctzl)
#define mbedtls_mpi_uint_ctz __builtin_ctzl
#elif (MBEDTLS_MPI_UINT_MAX == ULLONG_MAX) && __has_builtin(__builtin_ctzll)
#define mbedtls_mpi_uint_ctz __builtin_ctzll
#endif
#endif
#if defined(mbedtls_mpi_uint_ctz)
for (i = 0; i < X->n; i++) {
for (j = 0; j < biL; j++, count++) {
if (X->p[i] != 0) return i * biL + mbedtls_mpi_uint_ctz(X->p[i]);
}
#else
size_t count = 0;
for (i = 0; i < X->n; i++) {
for (size_t j = 0; j < biL; j++, count++) {
if (((X->p[i] >> j) & 1) != 0) {
return count;
}
}
}
#endif
return 0;
}