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add

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

timing_safe.add

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

File

lib/std/crypto/timing_safe.zig:82

Code

pub fn add(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 carry: u1 = 0;
    if (endian == .little) {
        var i: usize = 0;
        while (i < len) : (i += 1) {
            const ov1 = @addWithOverflow(a[i], b[i]);
            const ov2 = @addWithOverflow(ov1[0], carry);
            result[i] = ov2[0];
            carry = ov1[1] | ov2[1];
        }
    } else {
        var i: usize = len;
        while (i != 0) {
            i -= 1;
            const ov1 = @addWithOverflow(a[i], b[i]);
            const ov2 = @addWithOverflow(ov1[0], carry);
            result[i] = ov2[0];
            carry = ov1[1] | ov2[1];
        }
    }
    return @as(bool, @bitCast(carry));
}