bittest.cpp

来自「开放源码的编译器open watcom 1.6.0版的源代码」· C++ 代码 · 共 66 行

/****************************************************************************
*
*                            Open Watcom Project
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*    Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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*  ========================================================================
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*    This file contains Original Code and/or Modifications of Original
*    Code as defined in and that are subject to the Sybase Open Watcom
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* Description:  WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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****************************************************************************/


#include "cpplib.h"

static uint_8 mask_on[]         // bits mask for byte (set,test)
    = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };

static uint_8 mask_off[]        // bits mask for byte (reset)
    = { 0xFE, 0xFD, 0xFB, 0xF7, 0xEF, 0xDF, 0xBF, 0x7F };


extern "C"
uint_8 CPPLIB( bit_test )(      // TEST IF BIT IS ON
    uint_8* bits,               // - bits
    offset_t bit_no )           // - bit_no
{
    size_t offset;              // - offset within "bits"

    offset = bit_no / 8;
    bit_no -= ( offset * 8 );
    return (uint_8)( mask_on[ bit_no ] & bits[ offset ] );
}


extern "C"
void CPPLIB( bit_off )(         // TURN BIT OFF
    uint_8* bits,               // - bits
    offset_t bit_no )           // - bit_no
{
    size_t offset;              // - offset within "bits"

    offset = bit_no / 8;
    bit_no -= ( offset * 8 );
    bits[ offset ] &= mask_off[ bit_no ];
}