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Fixed handling of power operator

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This commit is contained in:
Clifford Wolf 2013-11-07 22:20:00 +01:00
parent d7cb62ac96
commit fc6dc0d7b8
4 changed files with 79 additions and 20 deletions
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52
kernel/calc.cc
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@ -17,6 +17,10 @@
*
*/
// [[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/log.h"
#include "kernel/rtlil.h"
#include "libs/bigint/BigIntegerLibrary.hh"
@ -450,21 +454,49 @@ RTLIL::Const RTLIL::const_pow(const RTLIL::Const &arg1, const RTLIL::Const &arg2
{
int undef_bit_pos = -1;
log("--POW--\n");
BigInteger a = const2big(arg1, signed1, undef_bit_pos);
BigInteger b = const2big(arg2, signed2, undef_bit_pos);
BigInteger y = 1;
if (b < 0 || a == 0) {
y = 0;
} else {
while (b > 0) {
y = y * a;
if (y.getLength() > 0x10000) {
undef_bit_pos = 0;
break;
}
b--;
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));