AuroraMiddleware/libtommath
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added shortcuts for bases that are powers of two

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czurnieden 2019-10-10 23:33:09 +02:00 committed by Steffen Jaeckel
parent 9bf8ce0322
commit f0a9d3c355
1 changed files with 14 additions and 3 deletions
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17
bn_mp_ilogb.c
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@ -78,9 +78,11 @@ mp_err mp_ilogb(const mp_int *a, uint32_t base, mp_int *c)
mp_int bracket_low, bracket_high, bracket_mid, t, bi_base;
err = MP_OKAY;
if (a->sign == MP_NEG) {
return MP_VAL;
}
if (MP_IS_ZERO(a)) {
return MP_VAL;
}
@ -88,10 +90,19 @@ mp_err mp_ilogb(const mp_int *a, uint32_t base, mp_int *c)
if (base < 2u) {
return MP_VAL;
}
if (base == 2u) {
mp_set_u32(c, (uint32_t)(mp_count_bits(a) - 1));
return err;
/* A small shortcut for bases that are powers of two. */
if (!(base & (base - 1u))) {
int x, y, bit_count;
for (y=0; (y < 7) && !(base & 1u); y++) {
base >>= 1;
}
bit_count = mp_count_bits(a) - 1;
x = bit_count/y;
mp_set_u32(c, (uint32_t)(x));
return MP_OKAY;
}
if (a->used == 1) {
mp_set(c, s_digit_ilogb(base, a->dp[0]));
return err;