Function timingSafeSub [src]

Alias for std.crypto.timing_safe.sub

Subtract two integers serialized as arrays of the same size, in constant time. The result is stored into result, and true is returned if an underflow occurred.

Prototype

pub fn sub(comptime T: type, a: []const T, b: []const T, result: []T, endian: Endian) bool

Parameters

T: typea: []const Tb: []const Tresult: []Tendian: Endian

Source

  pub fn sub(comptime T: type, a: []const T, b: []const T, result: []T, endian: Endian) bool {
    const len = a.len;
    assert(len == b.len and len == result.len);
    var borrow: u1 = 0;
    if (endian == .little) {
        var i: usize = 0;
        while (i < len) : (i += 1) {
            const ov1 = @subWithOverflow(a[i], b[i]);
            const ov2 = @subWithOverflow(ov1[0], borrow);
            result[i] = ov2[0];
            borrow = ov1[1] | ov2[1];
        }
    } else {
        var i: usize = len;
        while (i != 0) {
            i -= 1;
            const ov1 = @subWithOverflow(a[i], b[i]);
            const ov2 = @subWithOverflow(ov1[0], borrow);
            result[i] = ov2[0];
            borrow = ov1[1] | ov2[1];
        }
    }
    return @as(bool, @bitCast(borrow));
}  