Function eql [src]

Compares two arrays in constant time (for a given length) and returns whether they are equal. This function was designed to compare short cryptographic secrets (MACs, signatures). For all other applications, use mem.eql() instead.

Prototype

pub fn eql(comptime T: type, a: T, b: T) bool

Parameters

T: typea: Tb: T

Example

 test eql {
    const random = std.crypto.random;
    const expect = std.testing.expect;
    var a: [100]u8 = undefined;
    var b: [100]u8 = undefined;
    random.bytes(a[0..]);
    random.bytes(b[0..]);
    try expect(!eql([100]u8, a, b));
    a = b;
    try expect(eql([100]u8, a, b));
}

Source

  pub fn eql(comptime T: type, a: T, b: T) bool {
    switch (@typeInfo(T)) {
        .array => |info| {
            const C = info.child;
            if (@typeInfo(C) != .int) {
                @compileError("Elements to be compared must be integers");
            }
            var acc = @as(C, 0);
            for (a, 0..) |x, i| {
                acc |= x ^ b[i];
            }
            const s = @typeInfo(C).int.bits;
            const Cu = std.meta.Int(.unsigned, s);
            const Cext = std.meta.Int(.unsigned, s + 1);
            return @as(bool, @bitCast(@as(u1, @truncate((@as(Cext, @as(Cu, @bitCast(acc))) -% 1) >> s))));
        },
        .vector => |info| {
            const C = info.child;
            if (@typeInfo(C) != .int) {
                @compileError("Elements to be compared must be integers");
            }
            const acc = @reduce(.Or, a ^ b);
            const s = @typeInfo(C).int.bits;
            const Cu = std.meta.Int(.unsigned, s);
            const Cext = std.meta.Int(.unsigned, s + 1);
            return @as(bool, @bitCast(@as(u1, @truncate((@as(Cext, @as(Cu, @bitCast(acc))) -% 1) >> s))));
        },
        else => {
            @compileError("Only arrays and vectors can be compared");
        },
    }
}  