/
arith_uint256.cpp
74 lines (68 loc) · 2.16 KB
/
arith_uint256.cpp
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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin developers
// Copyright (c) 2017 The KORE developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include "arith_uint256.h"
#include "crypto/common.h"
#include "uint256.h"
#include "utilstrencodings.h"
#include <stdio.h>
#include <string.h>
// This implementation directly uses shifts instead of going
// through an intermediate MPI representation.
arith_uint256& arith_uint256::SetCompact(uint32_t nCompact, bool* pfNegative, bool* pfOverflow)
{
int nSize = nCompact >> 24;
uint32_t nWord = nCompact & 0x007fffff;
if (nSize <= 3) {
nWord >>= 8 * (3 - nSize);
*this = nWord;
} else {
*this = nWord;
*this <<= 8 * (nSize - 3);
}
if (pfNegative)
*pfNegative = nWord != 0 && (nCompact & 0x00800000) != 0;
if (pfOverflow)
*pfOverflow = nWord != 0 && ((nSize > 34) ||
(nWord > 0xff && nSize > 33) ||
(nWord > 0xffff && nSize > 32));
return *this;
}
uint32_t arith_uint256::GetCompact(bool fNegative) const
{
int nSize = (bits() + 7) / 8;
uint32_t nCompact = 0;
if (nSize <= 3) {
nCompact = GetLow64() << 8 * (3 - nSize);
} else {
arith_uint256 bn = *this >> 8 * (nSize - 3);
nCompact = bn.GetLow64();
}
// The 0x00800000 bit denotes the sign.
// Thus, if it is already set, divide the mantissa by 256 and increase the exponent.
if (nCompact & 0x00800000) {
nCompact >>= 8;
nSize++;
}
assert((nCompact & ~0x007fffff) == 0);
assert(nSize < 256);
nCompact |= nSize << 24;
nCompact |= (fNegative && (nCompact & 0x007fffff) ? 0x00800000 : 0);
return nCompact;
}
uint256 ArithToUint256(const arith_uint256 &a)
{
uint256 b;
for(int x=0; x<a.WIDTH; ++x)
WriteLE32(b.begin() + x*4, a.pn[x]);
return b;
}
arith_uint256 UintToArith256(const uint256 &a)
{
arith_uint256 b;
for(int x=0; x<b.WIDTH; ++x)
b.pn[x] = ReadLE32(a.begin() + x*4);
return b;
}