From 4c93bfe390719b8f42295bb9130213c8ad730809 Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Mon, 7 Sep 2026 21:02:55 +0200
Subject: [PATCH] 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.
---
 lib/std/crypto/ff.zig | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/std/crypto/ff.zig b/lib/std/crypto/ff.zig
index 4e599b67c48fff0e8f7241e821398ce36b2972e8..ea97d69f27aa4bb2ea27a8d35b3079a554028083 100644
--- a/lib/std/crypto/ff.zig
+++ b/lib/std/crypto/ff.zig
@@ -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(),
-                y.limbsConst(),
+                &x.limbs_buffer,
+                &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);
-- 
2.54.0