Zig 0.17.0-dev (Split by item)

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ScalarDouble

scalar.ScalarDouble

const ScalarDouble = struct

File

lib/std/crypto/pcurves/p384/scalar.zig:174

Code

const ScalarDouble = struct {
    x1: Fe,
    x2: Fe,

    fn fromBytes(comptime bits: usize, s_: [bits / 8]u8, endian: std.builtin.Endian) ScalarDouble {
        debug.assert(bits > 0 and bits <= 512 and bits >= Fe.saturated_bits and bits <= Fe.saturated_bits * 2);

        var s = s_;
        if (endian == .big) {
            for (s_, 0..) |x, i| s[s.len - 1 - i] = x;
        }
        var t = ScalarDouble{ .x1 = undefined, .x2 = Fe.zero };
        {
            var b: [encoded_length]u8 = @splat(0);
            const len = @min(s.len, 32);
            b[0..len].* = s[0..len].*;
            t.x1 = Fe.fromBytes(b, .little) catch unreachable;
        }
        if (s_.len >= 32) {
            var b: [encoded_length]u8 = @splat(0);
            const len = @min(s.len - 32, 32);
            b[0..len].* = s[32..][0..len].*;
            t.x2 = Fe.fromBytes(b, .little) catch unreachable;
        }
        return t;
    }

    fn reduce(expanded: ScalarDouble, comptime bits: usize) Scalar {
        debug.assert(bits > 0 and bits <= Fe.saturated_bits * 3 and bits <= 512);
        var fe = expanded.x1;
        if (bits >= 256) {
            const st1 = Fe.fromInt(1 << 256) catch unreachable;
            fe = fe.add(expanded.x2.mul(st1));
        }
        return Scalar{ .fe = fe };
    }
}