Документация по криптоалгоритмам / CRYPTO30 / misc

// misc.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "misc.h"
#include "words.h"

NAMESPACE_BEGIN(CryptoPP)

byte OAEP_P_DEFAULT[1];

void xorbuf(byte *buf, const byte *mask, unsigned int count)
{
	if (((unsigned int)buf | (unsigned int)mask | count) % WORD_SIZE == 0)
		XorWords((word *)buf, (const word *)mask, count/WORD_SIZE);
	else
	{
		for (unsigned int i=0; i<count; i++)
			buf[i] ^= mask[i];
	}
}

void xorbuf(byte *output, const byte *input, const byte *mask, unsigned int count)
{
	if (((unsigned int)output | (unsigned int)input | (unsigned int)mask | count) % WORD_SIZE == 0)
		XorWords((word *)output, (const word *)input, (const word *)mask, count/WORD_SIZE);
	else
	{
		for (unsigned int i=0; i<count; i++)
			output[i] = input[i] ^ mask[i];
	}
}

unsigned int Parity(unsigned long value)
{
	for (unsigned int i=8*sizeof(value)/2; i>0; i/=2)
		value ^= value >> i;
	return (unsigned int)value&1;
}

unsigned int BytePrecision(unsigned long value)
{
	unsigned int i;
	for (i=sizeof(value); i; --i)
		if (value >> (i-1)*8)
			break;

	return i;
}

unsigned int BitPrecision(unsigned long value)
{
	if (!value)
		return 0;

	unsigned int l=0, h=8*sizeof(value);

	while (h-l > 1)
	{
		unsigned int t = (l+h)/2;
		if (value >> t)
			l = t;
		else
			h = t;
	}

	return h;
}

unsigned long Crop(unsigned long value, int size)
{
	if (size < 8*sizeof(value))
    	return (value & ((1L << size) - 1));
	else
		return value;
}

NAMESPACE_END