Backend128_Tables

pub const Backend128_Tables = struct {
    const T = u128;
    const mulShift = mulShift128;
    const POW5_INV_BITCOUNT = FLOAT128_POW5_INV_BITCOUNT;
    const POW5_BITCOUNT = FLOAT128_POW5_BITCOUNT;

    const bound1 = 55;
    const bound2 = 127;
    const adjust_q = true;

    fn computePow5(i: u32) [4]u64 {
        const base = i / FLOAT128_POW5_TABLE_SIZE;
        const base2 = base * FLOAT128_POW5_TABLE_SIZE;
        const mul = &FLOAT128_POW5_SPLIT[base];
        if (i == base2) {
            return mul.*;
        } else {
            const offset = i - base2;
            const m = &FLOAT128_POW5_TABLE[offset];
            const delta = pow5Bits(i) - pow5Bits(base2);

            const shift: u6 = @intCast(2 * (i % 32));
            const corr: u32 = @intCast((FLOAT128_POW5_ERRORS[i / 32] >> shift) & 3);
            return mul_128_256_shift(m, mul, delta, corr);
        }
    }

    fn computeInvPow5(i: u32) [4]u64 {
        const base = (i + FLOAT128_POW5_TABLE_SIZE - 1) / FLOAT128_POW5_TABLE_SIZE;
        const base2 = base * FLOAT128_POW5_TABLE_SIZE;
        const mul = &FLOAT128_POW5_INV_SPLIT[base]; // 1 / 5^base2
        if (i == base2) {
            return .{ mul[0] + 1, mul[1], mul[2], mul[3] };
        } else {
            const offset = base2 - i;
            const m = &FLOAT128_POW5_TABLE[offset]; // 5^offset
            const delta = pow5Bits(base2) - pow5Bits(i);

            const shift: u6 = @intCast(2 * (i % 32));
            const corr: u32 = @intCast(((FLOAT128_POW5_INV_ERRORS[i / 32] >> shift) & 3) + 1);
            return mul_128_256_shift(m, mul, delta, corr);
        }
    }
}