Backend64_TablesSmall

pub const Backend64_TablesSmall = struct {
    const T = u64;
    const mulShift = mulShift64;
    const POW5_INV_BITCOUNT = FLOAT64_POW5_INV_BITCOUNT;
    const POW5_BITCOUNT = FLOAT64_POW5_BITCOUNT;

    const bound1 = 21;
    const bound2 = 63;
    const adjust_q = false;

    fn computePow5(i: u32) [2]u64 {
        const base = i / FLOAT64_POW5_TABLE_SIZE;
        const base2 = base * FLOAT64_POW5_TABLE_SIZE;
        const mul = &FLOAT64_POW5_SPLIT2[base];
        if (i == base2) {
            return .{ mul[0], mul[1] };
        } else {
            const offset = i - base2;
            const m = FLOAT64_POW5_TABLE[offset];
            const b0 = @as(u128, m) * mul[0];
            const b2 = @as(u128, m) * mul[1];
            const delta: u7 = @intCast(pow5Bits(i) - pow5Bits(base2));
            const shift: u5 = @intCast((i % 16) << 1);
            const shifted_sum = ((b0 >> delta) + (b2 << (64 - delta))) + 1 + ((FLOAT64_POW5_OFFSETS[i / 16] >> shift) & 3);
            return .{ @truncate(shifted_sum), @truncate(shifted_sum >> 64) };
        }
    }

    fn computeInvPow5(i: u32) [2]u64 {
        const base = (i + FLOAT64_POW5_TABLE_SIZE - 1) / FLOAT64_POW5_TABLE_SIZE;
        const base2 = base * FLOAT64_POW5_TABLE_SIZE;
        const mul = &FLOAT64_POW5_INV_SPLIT2[base]; // 1 / 5^base2
        if (i == base2) {
            return .{ mul[0], mul[1] };
        } else {
            const offset = base2 - i;
            const m = FLOAT64_POW5_TABLE[offset]; // 5^offset
            const b0 = @as(u128, m) * (mul[0] - 1);
            const b2 = @as(u128, m) * mul[1]; // 1/5^base2 * 5^offset = 1/5^(base2-offset) = 1/5^i
            const delta: u7 = @intCast(pow5Bits(base2) - pow5Bits(i));
            const shift: u5 = @intCast((i % 16) << 1);
            const shifted_sum = ((b0 >> delta) + (b2 << (64 - delta))) + 1 + ((FLOAT64_POW5_INV_OFFSETS[i / 16] >> shift) & 3);
            return .{ @truncate(shifted_sum), @truncate(shifted_sum >> 64) };
        }
    }
}