Commit 4c93bfe390719b8f42295bb9130213c8ad730809 | zig

author	Frank Denis <124872+jedisct1@users.noreply.github.com> 2026-09-07 21:02:55+02:00
committer	Frank Denis <124872+jedisct1@users.noreply.github.com> 2026-09-24 20:06:04+02:00
log	4c93bfe390719b8f42295bb9130213c8ad730809
tree	7de178905d6e2c64746400e69a05d94f774cd07b
parent	392b17125475fd955ae591107ae92458c4bc1c4f

crypto.ff: compare full Uint buffers and add a isOne() function

Compare the full zero-padded buffers so we can support different
active widths and still keep the comparison length fixed at comptime.

Also add a constant-time isOne() check, which is quite useful for
a long of applications using finite field arithemtic.

1 files changed, 7 insertions(+), 2 deletions(-)

lib
- std
  - crypto
    ff.zig

lib/std/crypto/ff.zig+7-2

 @@ -207,8 +207,8 @@ pub fn Uint(comptime max_bits: comptime_int) type {
         pub fn compare(x: Self, y: Self) math.Order {
             return crypto.timing_safe.compare(
                 Limb,
-                x.limbsConst(),
+                &x.limbs_buffer,
-                y.limbsConst(),
+                &y.limbs_buffer,
                 .little,
             );
         }
 @@ -223,6 +223,11 @@ pub fn Uint(comptime max_bits: comptime_int) type {
             return @as(u1, @truncate(x.limbsConst()[0])) != 0;
         }
+        pub fn isOne(x: Self) bool {
+            const x_limbs = x.limbsConst();
+            return ct.eql((x_limbs[0] ^ 1) | orLimbs(x_limbs[1..]), 0);
+        }
         /// Adds `y` to `x`, and returns `true` if the operation overflowed.
         pub fn addWithOverflow(x: *Self, y: Self) u1 {
             return x.conditionalAddWithOverflow(true, y);