calc.cc

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/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
 *  
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *  
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

// [[CITE]] Power-Modulus Algorithm
// Schneier, Bruce (1996). Applied Cryptography: Protocols, Algorithms, and Source Code in C,
// Second Edition (2nd ed.). Wiley. ISBN 978-0-471-11709-4, page 244

#include "kernel/yosys.h"
#include "libs/bigint/BigIntegerLibrary.hh"

YOSYS_NAMESPACE_BEGIN

static void extend_u0(RTLIL::Const &arg, int width, bool is_signed)
{
    RTLIL::State padding = RTLIL::State::S0;

    if (arg.bits.size() > 0 && is_signed)
        padding = arg.bits.back();

    while (int(arg.bits.size()) < width)
        arg.bits.push_back(padding);

    arg.bits.resize(width);
}

static BigInteger const2big(const RTLIL::Const &val, bool as_signed, int &undef_bit_pos)
{
    BigInteger result = 0, this_bit = 1;
    for (size_t i = 0; i < val.bits.size(); i++) {
        if (val.bits[i] == RTLIL::State::S1) {
            if (as_signed && i+1 == val.bits.size())
                result -= this_bit;
            else
                result += this_bit;
        }
        else if (val.bits[i] != RTLIL::State::S0) {
            if (undef_bit_pos < 0)
                undef_bit_pos = i;
        }
        this_bit *= 2;
    }
    return result;
}

static RTLIL::Const big2const(const BigInteger &val, int result_len, int undef_bit_pos)
{
    if (undef_bit_pos >= 0)
        return RTLIL::Const(RTLIL::State::Sx, result_len);

    BigUnsigned mag = val.getMagnitude();
    RTLIL::Const result(0, result_len);

    if (!mag.isZero())
    {
        if (val.getSign() < 0)
        {
            mag--;
            for (int i = 0; i < result_len; i++)
                result.bits[i] = mag.getBit(i) ? RTLIL::State::S0 : RTLIL::State::S1;
        }
        else
        {
            for (int i = 0; i < result_len; i++)
                result.bits[i] = mag.getBit(i) ? RTLIL::State::S1 : RTLIL::State::S0;
        }
    }

#if 0
    if (undef_bit_pos >= 0)
        for (int i = undef_bit_pos; i < result_len; i++)
            result.bits[i] = RTLIL::State::Sx;
#endif

    return result;
}

static RTLIL::State logic_and(RTLIL::State a, RTLIL::State b)
{
    if (a == RTLIL::State::S0) return RTLIL::State::S0;
    if (b == RTLIL::State::S0) return RTLIL::State::S0;
    if (a != RTLIL::State::S1) return RTLIL::State::Sx;
    if (b != RTLIL::State::S1) return RTLIL::State::Sx;
    return RTLIL::State::S1;
}

static RTLIL::State logic_or(RTLIL::State a, RTLIL::State b)
{
    if (a == RTLIL::State::S1) return RTLIL::State::S1;
    if (b == RTLIL::State::S1) return RTLIL::State::S1;
    if (a != RTLIL::State::S0) return RTLIL::State::Sx;
    if (b != RTLIL::State::S0) return RTLIL::State::Sx;
    return RTLIL::State::S0;
}

static RTLIL::State logic_xor(RTLIL::State a, RTLIL::State b)
{
    if (a != RTLIL::State::S0 && a != RTLIL::State::S1) return RTLIL::State::Sx;
    if (b != RTLIL::State::S0 && b != RTLIL::State::S1) return RTLIL::State::Sx;
    return a != b ? RTLIL::State::S1 : RTLIL::State::S0;
}

static RTLIL::State logic_xnor(RTLIL::State a, RTLIL::State b)
{
    if (a != RTLIL::State::S0 && a != RTLIL::State::S1) return RTLIL::State::Sx;
    if (b != RTLIL::State::S0 && b != RTLIL::State::S1) return RTLIL::State::Sx;
    return a == b ? RTLIL::State::S1 : RTLIL::State::S0;
}

RTLIL::Const RTLIL::const_not(const RTLIL::Const &arg1, const RTLIL::Const&, bool signed1, bool, int result_len)
{
    if (result_len < 0)
        result_len = arg1.bits.size();

    RTLIL::Const arg1_ext = arg1;
    extend_u0(arg1_ext, result_len, signed1);

    RTLIL::Const result(RTLIL::State::Sx, result_len);
    for (size_t i = 0; i < size_t(result_len); i++) {
        if (i >= arg1_ext.bits.size())
            result.bits[i] = RTLIL::State::S0;
        else if (arg1_ext.bits[i] == RTLIL::State::S0)
            result.bits[i] = RTLIL::State::S1;
        else if (arg1_ext.bits[i] == RTLIL::State::S1)
            result.bits[i] = RTLIL::State::S0;
    }

    return result;
}

static RTLIL::Const logic_wrapper(RTLIL::State(*logic_func)(RTLIL::State, RTLIL::State),
        RTLIL::Const arg1, RTLIL::Const arg2, bool signed1, bool signed2, int result_len = -1)
{
    if (result_len < 0)
        result_len = std::max(arg1.bits.size(), arg2.bits.size());

    extend_u0(arg1, result_len, signed1);
    extend_u0(arg2, result_len, signed2);

    RTLIL::Const result(RTLIL::State::Sx, result_len);
    for (size_t i = 0; i < size_t(result_len); i++) {
        RTLIL::State a = i < arg1.bits.size() ? arg1.bits[i] : RTLIL::State::S0;
        RTLIL::State b = i < arg2.bits.size() ? arg2.bits[i] : RTLIL::State::S0;
        result.bits[i] = logic_func(a, b);
    }

    return result;
}

RTLIL::Const RTLIL::const_and(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return logic_wrapper(logic_and, arg1, arg2, signed1, signed2, result_len);
}

RTLIL::Const RTLIL::const_or(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return logic_wrapper(logic_or, arg1, arg2, signed1, signed2, result_len);
}

RTLIL::Const RTLIL::const_xor(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return logic_wrapper(logic_xor, arg1, arg2, signed1, signed2, result_len);
}

RTLIL::Const RTLIL::const_xnor(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return logic_wrapper(logic_xnor, arg1, arg2, signed1, signed2, result_len);
}

static RTLIL::Const logic_reduce_wrapper(RTLIL::State initial, RTLIL::State(*logic_func)(RTLIL::State, RTLIL::State), const RTLIL::Const &arg1, int result_len)
{
    RTLIL::State temp = initial;

    for (size_t i = 0; i < arg1.bits.size(); i++)
        temp = logic_func(temp, arg1.bits[i]);

    RTLIL::Const result(temp);
    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_reduce_and(const RTLIL::Const &arg1, const RTLIL::Const&, bool, bool, int result_len)
{
    return logic_reduce_wrapper(RTLIL::State::S1, logic_and, arg1, result_len);
}

RTLIL::Const RTLIL::const_reduce_or(const RTLIL::Const &arg1, const RTLIL::Const&, bool, bool, int result_len)
{
    return logic_reduce_wrapper(RTLIL::State::S0, logic_or, arg1, result_len);
}

RTLIL::Const RTLIL::const_reduce_xor(const RTLIL::Const &arg1, const RTLIL::Const&, bool, bool, int result_len)
{
    return logic_reduce_wrapper(RTLIL::State::S0, logic_xor, arg1, result_len);
}

RTLIL::Const RTLIL::const_reduce_xnor(const RTLIL::Const &arg1, const RTLIL::Const&, bool, bool, int result_len)
{
    RTLIL::Const buffer = logic_reduce_wrapper(RTLIL::State::S0, logic_xor, arg1, result_len);
    if (!buffer.bits.empty()) {
        if (buffer.bits.front() == RTLIL::State::S0)
            buffer.bits.front() = RTLIL::State::S1;
        else if (buffer.bits.front() == RTLIL::State::S1)
            buffer.bits.front() = RTLIL::State::S0;
    }
    return buffer;
}

RTLIL::Const RTLIL::const_reduce_bool(const RTLIL::Const &arg1, const RTLIL::Const&, bool, bool, int result_len)
{
    return logic_reduce_wrapper(RTLIL::State::S0, logic_or, arg1, result_len);
}

RTLIL::Const RTLIL::const_logic_not(const RTLIL::Const &arg1, const RTLIL::Const&, bool signed1, bool, int result_len)
{
    int undef_bit_pos_a = -1;
    BigInteger a = const2big(arg1, signed1, undef_bit_pos_a);
    RTLIL::Const result(a.isZero() ? undef_bit_pos_a >= 0 ? RTLIL::State::Sx : RTLIL::State::S1 : RTLIL::State::S0);

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_logic_and(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos_a = -1, undef_bit_pos_b = -1;
    BigInteger a = const2big(arg1, signed1, undef_bit_pos_a);
    BigInteger b = const2big(arg2, signed2, undef_bit_pos_b);

    RTLIL::State bit_a = a.isZero() ? undef_bit_pos_a >= 0 ? RTLIL::State::Sx : RTLIL::State::S0 : RTLIL::State::S1;
    RTLIL::State bit_b = b.isZero() ? undef_bit_pos_b >= 0 ? RTLIL::State::Sx : RTLIL::State::S0 : RTLIL::State::S1;
    RTLIL::Const result(logic_and(bit_a, bit_b));

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_logic_or(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos_a = -1, undef_bit_pos_b = -1;
    BigInteger a = const2big(arg1, signed1, undef_bit_pos_a);
    BigInteger b = const2big(arg2, signed2, undef_bit_pos_b);

    RTLIL::State bit_a = a.isZero() ? undef_bit_pos_a >= 0 ? RTLIL::State::Sx : RTLIL::State::S0 : RTLIL::State::S1;
    RTLIL::State bit_b = b.isZero() ? undef_bit_pos_b >= 0 ? RTLIL::State::Sx : RTLIL::State::S0 : RTLIL::State::S1;
    RTLIL::Const result(logic_or(bit_a, bit_b));

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

static RTLIL::Const const_shift_worker(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool sign_ext, int direction, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger offset = const2big(arg2, false, undef_bit_pos) * direction;

    if (result_len < 0)
        result_len = arg1.bits.size();

    RTLIL::Const result(RTLIL::State::Sx, result_len);
    if (undef_bit_pos >= 0)
        return result;

    for (int i = 0; i < result_len; i++) {
        BigInteger pos = BigInteger(i) + offset;
        if (pos < 0)
            result.bits[i] = RTLIL::State::S0;
        else if (pos >= arg1.bits.size())
            result.bits[i] = sign_ext ? arg1.bits.back() : RTLIL::State::S0;
        else
            result.bits[i] = arg1.bits[pos.toInt()];
    }

    return result;
}

RTLIL::Const RTLIL::const_shl(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    extend_u0(arg1_ext, result_len, signed1);
    return const_shift_worker(arg1_ext, arg2, false, -1, result_len);
}

RTLIL::Const RTLIL::const_shr(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    extend_u0(arg1_ext, std::max(result_len, GetSize(arg1)), signed1);
    return const_shift_worker(arg1_ext, arg2, false, +1, result_len);
}

RTLIL::Const RTLIL::const_sshl(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    if (!signed1)
        return const_shl(arg1, arg2, signed1, signed2, result_len);
    return const_shift_worker(arg1, arg2, true, -1, result_len);
}

RTLIL::Const RTLIL::const_sshr(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    if (!signed1)
        return const_shr(arg1, arg2, signed1, signed2, result_len);
    return const_shift_worker(arg1, arg2, true, +1, result_len);
}

static RTLIL::Const const_shift_shiftx(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool, bool signed2, int result_len, RTLIL::State other_bits)
{
    int undef_bit_pos = -1;
    BigInteger offset = const2big(arg2, signed2, undef_bit_pos);

    if (result_len < 0)
        result_len = arg1.bits.size();

    RTLIL::Const result(RTLIL::State::Sx, result_len);
    if (undef_bit_pos >= 0)
        return result;

    for (int i = 0; i < result_len; i++) {
        BigInteger pos = BigInteger(i) + offset;
        if (pos < 0 || pos >= arg1.bits.size())
            result.bits[i] = other_bits;
        else
            result.bits[i] = arg1.bits[pos.toInt()];
    }

    return result;
}

RTLIL::Const RTLIL::const_shift(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return const_shift_shiftx(arg1, arg2, signed1, signed2, result_len, RTLIL::State::S0);
}

RTLIL::Const RTLIL::const_shiftx(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    return const_shift_shiftx(arg1, arg2, signed1, signed2, result_len, RTLIL::State::Sx);
}

RTLIL::Const RTLIL::const_lt(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    bool y = const2big(arg1, signed1, undef_bit_pos) < const2big(arg2, signed2, undef_bit_pos);
    RTLIL::Const result(undef_bit_pos >= 0 ? RTLIL::State::Sx : y ? RTLIL::State::S1 : RTLIL::State::S0);

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_le(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    bool y = const2big(arg1, signed1, undef_bit_pos) <= const2big(arg2, signed2, undef_bit_pos);
    RTLIL::Const result(undef_bit_pos >= 0 ? RTLIL::State::Sx : y ? RTLIL::State::S1 : RTLIL::State::S0);

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_eq(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    RTLIL::Const arg2_ext = arg2;
    RTLIL::Const result(RTLIL::State::S0, result_len);

    int width = std::max(arg1_ext.bits.size(), arg2_ext.bits.size());
    extend_u0(arg1_ext, width, signed1 && signed2);
    extend_u0(arg2_ext, width, signed1 && signed2);

    RTLIL::State matched_status = RTLIL::State::S1;
    for (size_t i = 0; i < arg1_ext.bits.size(); i++) {
        if (arg1_ext.bits.at(i) == RTLIL::State::S0 && arg2_ext.bits.at(i) == RTLIL::State::S1)
            return result;
        if (arg1_ext.bits.at(i) == RTLIL::State::S1 && arg2_ext.bits.at(i) == RTLIL::State::S0)
            return result;
        if (arg1_ext.bits.at(i) > RTLIL::State::S1 || arg2_ext.bits.at(i) > RTLIL::State::S1)
            matched_status = RTLIL::State::Sx;
    }

    result.bits.front() = matched_status;
    return result;
}

RTLIL::Const RTLIL::const_ne(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    RTLIL::Const result = RTLIL::const_eq(arg1, arg2, signed1, signed2, result_len);
    if (result.bits.front() == RTLIL::State::S0)
        result.bits.front() = RTLIL::State::S1;
    else if (result.bits.front() == RTLIL::State::S1)
        result.bits.front() = RTLIL::State::S0;
    return result;
}

RTLIL::Const RTLIL::const_eqx(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    RTLIL::Const arg2_ext = arg2;
    RTLIL::Const result(RTLIL::State::S0, result_len);

    int width = std::max(arg1_ext.bits.size(), arg2_ext.bits.size());
    extend_u0(arg1_ext, width, signed1 && signed2);
    extend_u0(arg2_ext, width, signed1 && signed2);

    for (size_t i = 0; i < arg1_ext.bits.size(); i++) {
        if (arg1_ext.bits.at(i) != arg2_ext.bits.at(i))
            return result;
    }

    result.bits.front() = RTLIL::State::S1;
    return result;
}

RTLIL::Const RTLIL::const_nex(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    RTLIL::Const result = RTLIL::const_eqx(arg1, arg2, signed1, signed2, result_len);
    if (result.bits.front() == RTLIL::State::S0)
        result.bits.front() = RTLIL::State::S1;
    else if (result.bits.front() == RTLIL::State::S1)
        result.bits.front() = RTLIL::State::S0;
    return result;
}

RTLIL::Const RTLIL::const_ge(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    bool y = const2big(arg1, signed1, undef_bit_pos) >= const2big(arg2, signed2, undef_bit_pos);
    RTLIL::Const result(undef_bit_pos >= 0 ? RTLIL::State::Sx : y ? RTLIL::State::S1 : RTLIL::State::S0);

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_gt(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    bool y = const2big(arg1, signed1, undef_bit_pos) > const2big(arg2, signed2, undef_bit_pos);
    RTLIL::Const result(undef_bit_pos >= 0 ? RTLIL::State::Sx : y ? RTLIL::State::S1 : RTLIL::State::S0);

    while (int(result.bits.size()) < result_len)
        result.bits.push_back(RTLIL::State::S0);
    return result;
}

RTLIL::Const RTLIL::const_add(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger y = const2big(arg1, signed1, undef_bit_pos) + const2big(arg2, signed2, undef_bit_pos);
    return big2const(y, result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), undef_bit_pos);
}

RTLIL::Const RTLIL::const_sub(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger y = const2big(arg1, signed1, undef_bit_pos) - const2big(arg2, signed2, undef_bit_pos);
    return big2const(y, result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), undef_bit_pos);
}

RTLIL::Const RTLIL::const_mul(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger y = const2big(arg1, signed1, undef_bit_pos) * const2big(arg2, signed2, undef_bit_pos);
    return big2const(y, result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), std::min(undef_bit_pos, 0));
}

RTLIL::Const RTLIL::const_div(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger a = const2big(arg1, signed1, undef_bit_pos);
    BigInteger b = const2big(arg2, signed2, undef_bit_pos);
    if (b.isZero())
        return RTLIL::Const(RTLIL::State::Sx, result_len);
    bool result_neg = (a.getSign() == BigInteger::negative) != (b.getSign() == BigInteger::negative);
    a = a.getSign() == BigInteger::negative ? -a : a;
    b = b.getSign() == BigInteger::negative ? -b : b;
    return big2const(result_neg ? -(a / b) : (a / b), result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), std::min(undef_bit_pos, 0));
}

RTLIL::Const RTLIL::const_mod(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;
    BigInteger a = const2big(arg1, signed1, undef_bit_pos);
    BigInteger b = const2big(arg2, signed2, undef_bit_pos);
    if (b.isZero())
        return RTLIL::Const(RTLIL::State::Sx, result_len);
    bool result_neg = a.getSign() == BigInteger::negative;
    a = a.getSign() == BigInteger::negative ? -a : a;
    b = b.getSign() == BigInteger::negative ? -b : b;
    return big2const(result_neg ? -(a % b) : (a % b), result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), std::min(undef_bit_pos, 0));
}

RTLIL::Const RTLIL::const_pow(const RTLIL::Const &arg1, const RTLIL::Const &arg2, bool signed1, bool signed2, int result_len)
{
    int undef_bit_pos = -1;

    BigInteger a = const2big(arg1, signed1, undef_bit_pos);
    BigInteger b = const2big(arg2, signed2, undef_bit_pos);
    BigInteger y = 1;

    if (a == 0 && b < 0)
        return RTLIL::Const(RTLIL::State::Sx, result_len);

    if (a == 0 && b > 0)
        return RTLIL::Const(RTLIL::State::S0, result_len);

    if (b < 0)
    {
        if (a < -1 || a > 1)
            y = 0;
        if (a == -1)
            y = (-b % 2) == 0 ? 1 : -1;
    }

    if (b > 0)
    {
        // Power-modulo with 2^result_len as modulus
        BigInteger modulus = 1;
        int modulus_bits = (result_len >= 0 ? result_len : 1024);
        for (int i = 0; i < modulus_bits; i++)
            modulus *= 2;

        bool flip_result_sign = false;
        if (a < 0) {
            a *= -1;
            if (b % 2 == 1)
                flip_result_sign = true;
        }

        while (b > 0) {
            if (b % 2 == 1)
                y = (y * a) % modulus;
            b = b / 2;
            a = (a * a) % modulus;
        }

        if (flip_result_sign)
            y *= -1;
    }

    return big2const(y, result_len >= 0 ? result_len : std::max(arg1.bits.size(), arg2.bits.size()), std::min(undef_bit_pos, 0));
}

RTLIL::Const RTLIL::const_pos(const RTLIL::Const &arg1, const RTLIL::Const&, bool signed1, bool, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    extend_u0(arg1_ext, result_len, signed1);

    return arg1_ext;
}

RTLIL::Const RTLIL::const_neg(const RTLIL::Const &arg1, const RTLIL::Const&, bool signed1, bool, int result_len)
{
    RTLIL::Const arg1_ext = arg1;
    RTLIL::Const zero(RTLIL::State::S0, 1);

    return RTLIL::const_sub(zero, arg1_ext, true, signed1, result_len);
}

YOSYS_NAMESPACE_END