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feat: add num_bits() function (#570)

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## Describe the changes

adding a `num_bits()` function similar to
dcf73a5f96/ff/src/biginteger/mod.rs (L482)

this could be useful for small field optimizations

## Linked Issues

Resolves #
This commit is contained in:
Ethan-000
2024-08-07 07:37:16 +01:00
committed by GitHub
parent badb8c5d68
commit 621676bd41
1 changed files with 13 additions and 0 deletions
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13
icicle/include/fields/field.cuh
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@@ -124,6 +124,19 @@ public:
*/ */
static constexpr HOST_DEVICE_INLINE unsigned num_of_reductions() { return CONFIG::num_of_reductions; } static constexpr HOST_DEVICE_INLINE unsigned num_of_reductions() { return CONFIG::num_of_reductions; }
// count number of bits of the field element without leading zeros.
static constexpr HOST_DEVICE_INLINE unsigned num_bits(const Field& x)
{
size_t size = sizeof(x.limbs_storage.limbs[0]) * 8;
unsigned ret = size * TLC;
for (unsigned i = TLC; i-- > 0;) {
int leading = __clz(x.limbs_storage.limbs[i]);
ret -= leading;
if (leading != size) { break; }
}
return ret;
}
static constexpr unsigned slack_bits = 32 * TLC - NBITS; static constexpr unsigned slack_bits = 32 * TLC - NBITS;
struct Wide { struct Wide {