polyUnpackLeGamma1

fn polyUnpackLeGamma1(comptime gamma1_bits: u8, buf: []const u8) Poly

File

Code

fn polyUnpackLeGamma1(comptime gamma1_bits: u8, buf: []const u8) Poly {
    const gamma1: u32 = @as(u32, 1) << gamma1_bits;
    var p = Poly.zero;

    if (gamma1_bits == 17) {
        // Unpack 4 coefficients from 9 bytes (18 bits each)
        var j: usize = 0;
        var i: usize = 0;
        while (i < buf.len) : (i += 9) {
            var p0 = @as(u32, buf[i]) | (@as(u32, buf[i + 1]) << 8) | ((@as(u32, buf[i + 2]) & 0x3) << 16);
            var p1 = (@as(u32, buf[i + 2]) >> 2) | (@as(u32, buf[i + 3]) << 6) | ((@as(u32, buf[i + 4]) & 0xf) << 14);
            var p2 = (@as(u32, buf[i + 4]) >> 4) | (@as(u32, buf[i + 5]) << 4) | ((@as(u32, buf[i + 6]) & 0x3f) << 12);
            var p3 = (@as(u32, buf[i + 6]) >> 6) | (@as(u32, buf[i + 7]) << 2) | (@as(u32, buf[i + 8]) << 10);

            // Convert from [0, 2γ₁) to (-γ₁, γ₁]
            p0 = centeredToPositive(p0, gamma1);
            p1 = centeredToPositive(p1, gamma1);
            p2 = centeredToPositive(p2, gamma1);
            p3 = centeredToPositive(p3, gamma1);

            p.cs[j] = p0;
            p.cs[j + 1] = p1;
            p.cs[j + 2] = p2;
            p.cs[j + 3] = p3;

            j += 4;
        }
    } else if (gamma1_bits == 19) {
        // Unpack 2 coefficients from 5 bytes (20 bits each)
        var j: usize = 0;
        var i: usize = 0;
        while (i < buf.len) : (i += 5) {
            var p0 = @as(u32, buf[i]) | (@as(u32, buf[i + 1]) << 8) | ((@as(u32, buf[i + 2]) & 0xf) << 16);
            var p1 = (@as(u32, buf[i + 2]) >> 4) | (@as(u32, buf[i + 3]) << 4) | (@as(u32, buf[i + 4]) << 12);

            p0 = centeredToPositive(p0, gamma1);
            p1 = centeredToPositive(p1, gamma1);

            p.cs[j] = p0;
            p.cs[j + 1] = p1;

            j += 2;
        }
    } else {
        @compileError("gamma1_bits must be 17 or 19");
    }

    return p;
}