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Tricks of the Windows Gam…ming Gurus (2nd Edition)
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Disc2.iso
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vc98
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crt
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src
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rotl.c
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C/C++ Source or Header
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1998-06-17
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2KB
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77 lines
/***
*rotl.c - rotate an unsigned integer left
*
* Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* defines _rotl() - performs a rotate left on an unsigned integer.
*
*******************************************************************************/
#include <cruntime.h>
#include <stdlib.h>
#include <limits.h>
#ifdef _MSC_VER
#pragma function(_lrotl,_rotl)
#endif /* _MSC_VER */
#if UINT_MAX != 0xffffffff
#error This module assumes 32-bit integers
#endif /* UINT_MAX != 0xffffffff */
#if UINT_MAX != ULONG_MAX
#error This module assumes sizeof(int) == sizeof(long)
#endif /* UINT_MAX != ULONG_MAX */
/***
*unsigned _rotl(val, shift) - int rotate left
*
*Purpose:
* Performs a rotate left on an unsigned integer.
*
* [Note: The _lrotl entry is based on the assumption
* that sizeof(int) == sizeof(long).]
*Entry:
* unsigned val: value to rotate
* int shift: number of bits to shift by
*
*Exit:
* returns rotated value
*
*Exceptions:
* None.
*
*******************************************************************************/
unsigned long __cdecl _lrotl (
unsigned long val,
int shift
)
{
return( (unsigned long) _rotl((unsigned) val, shift) );
}
unsigned __cdecl _rotl (
unsigned val,
int shift
)
{
register unsigned hibit; /* non-zero means hi bit set */
register unsigned num = val; /* number to rotate */
shift &= 0x1f; /* modulo 32 -- this will also make
negative shifts work */
while (shift--) {
hibit = num & 0x80000000; /* get high bit */
num <<= 1; /* shift left one bit */
if (hibit)
num |= 1; /* set lo bit if hi bit was set */
}
return num;
}