Zig 0.17.0-dev (Split by item)

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ct_unprotected

ff.ct_unprotected

const ct_unprotected = struct

File

lib/std/crypto/ff.zig:926

Code

const ct_unprotected = struct {
    // Returns x if on is true, otherwise y.
    fn select(on: bool, x: Limb, y: Limb) Limb {
        return if (on) x else y;
    }

    // Compares two values in constant time.
    fn eql(x: anytype, y: @TypeOf(x)) bool {
        return x == y;
    }

    // Compares two big integers in constant time, returning true if x < y.
    fn limbsCmpLt(x: anytype, y: @TypeOf(x)) bool {
        const x_limbs = x.limbsConst();
        const y_limbs = y.limbsConst();
        assert(x_limbs.len == y_limbs.len);

        var i = x_limbs.len;
        while (i != 0) {
            i -= 1;
            if (x_limbs[i] != y_limbs[i]) {
                return x_limbs[i] < y_limbs[i];
            }
        }
        return false;
    }

    // Compares two big integers in constant time, returning true if x >= y.
    fn limbsCmpGeq(x: anytype, y: @TypeOf(x)) bool {
        return !limbsCmpLt(x, y);
    }

    // Multiplies two limbs and returns the result as a wide limb.
    fn mulWide(x: Limb, y: Limb) WideLimb {
        const wide = math.mulWide(Limb, x, y);
        return .{
            .hi = @as(Limb, @truncate(wide >> @typeInfo(Limb).int.bits)),
            .lo = @as(Limb, @truncate(wide)),
        };
    }
}