Zig 0.17.0-dev (Split by item)

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eql

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.

timing_safe.eql

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

File

lib/std/crypto/timing_safe.zig:12

Code

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 = @Int(.unsigned, s);
            const Cext = @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 = @Int(.unsigned, s);
            const Cext = @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");
        },
    }
}