Zig 0.17.0-dev (Split by item)

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compare

Compare two integers serialized as arrays of the same size, in constant time. Returns .lt if a<b, .gt if a>b and .eq if a=b

timing_safe.compare

pub fn compare(comptime T: type, a: []const T, b: []const T, endian: Endian) Order

File

lib/std/crypto/timing_safe.zig:47

Code

pub fn compare(comptime T: type, a: []const T, b: []const T, endian: Endian) Order {
    assert(a.len == b.len);
    const bits = switch (@typeInfo(T)) {
        .int => |cinfo| if (cinfo.signedness != .unsigned) @compileError("Elements to be compared must be unsigned") else cinfo.bits,
        else => @compileError("Elements to be compared must be integers"),
    };
    const Cext = @Int(.unsigned, bits + 1);
    var gt: T = 0;
    var eq: T = 1;
    if (endian == .little) {
        var i = a.len;
        while (i != 0) {
            i -= 1;
            const x1 = a[i];
            const x2 = b[i];
            gt |= @as(T, @truncate((@as(Cext, x2) -% @as(Cext, x1)) >> bits)) & eq;
            eq &= @as(T, @truncate((@as(Cext, (x2 ^ x1)) -% 1) >> bits));
        }
    } else {
        for (a, 0..) |x1, i| {
            const x2 = b[i];
            gt |= @as(T, @truncate((@as(Cext, x2) -% @as(Cext, x1)) >> bits)) & eq;
            eq &= @as(T, @truncate((@as(Cext, (x2 ^ x1)) -% 1) >> bits));
        }
    }
    if (gt != 0) {
        return Order.gt;
    } else if (eq != 0) {
        return Order.eq;
    }
    return Order.lt;
}