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/*
* Copyright (C) 1985-1992 New York University
*
* This file is part of the Ada/Ed-C system. See the Ada/Ed README file for
* warranty (none) and distribution info and also the GNU General Public
* License for more details.
*/
/* machine.c - procedures which optionally may be recoded in assembly language
*
* This file contains procedures which perform the integer arithmetic
* operations (addition, subtraction and multiplication) which require
* overflow detection of the result. C does not provide an efficient
* mechanism for catching overflows, so this is accomplished by doing
* some checking of the signs of the operands and result.
*
* A more appropriate mechanism, would be to have this computation and
* overflow check written in assembly language, where more control of
* the overflow bit can be realized.
*
* Each of the arithmetic procedures accept three parameters. The first
* two are the operands and the third is a pointer to an int representating
* a flag indicating whether there was an overflow in the operation or not.
*
* All of the arithmetic procedures can be compiled as is, however
* if there is a desire for an more efficient implementation assembly
* routine can be supplied which will supercede the C versions. If
* this is done you must define the appropriate symbolic name immediately
* below to avoid compiling the c prototype code. For example, once
* word_add is done in assembly, insert a define for WORD_ADD under
* an "ifdef" for the appropriate machine (sun, vax, etc) as is shown
* for the IBM_PC case below.
*
* MOVE_MEM is included here only because some run-time libraries might
* contain a routine which does the equivalent job and therefore could
* be substituted for the C code given here for it.
*/
#include "config.h"
#include "machineprots.h"
/*
* macros used to check for overflow condition on integer addition and
* subtraction. We assume twos complement arithmetic with wraparound on
* overflow
*/
#define sign(x) (x < 0 ? 1 : 0)
#define addoverflow(op1,op2,res) (sign(op1)==sign(op2) && sign(res)!=sign(op1))
#define suboverflow(op1,op2,res) (sign(op1)!=sign(op2) && sign(res)!=sign(op1))
#ifndef WORD_ADD
int word_add(int a, int b, int *overflow) /*;word_add*/
{
/* add with overflow check */
register int r;
r = a + b;
*overflow = addoverflow(a, b, r);
return r;
}
#endif
#ifndef WORD_SUB
int word_sub(int a, int b, int *overflow) /*;word_sub*/
{
/* subtract with overflow check */
register int r;
r = a - b;
*overflow = suboverflow(a, b, r);
return r;
}
#endif
#ifndef WORD_MUL
int word_mul(int a, int b, int *overflow) /*;word_mul*/
{
/* multiply with overflow check */
register int r;
if(a) {
r = a * b;
*overflow = (b != r/a) || (a == -1 && b < 0 && r < 0);
}
else {
*overflow = r = 0;
}
return r;
}
#endif
#ifndef LONG_ADD
long long_add(long a, long b, int *overflow) /*;long_add*/
{
/* add with overflow check */
register long r;
r = a + b;
*overflow = addoverflow(a, b, r);
return r;
}
#endif
#ifndef LONG_SUB
long long_sub(long a, long b, int *overflow) /*;long_sub*/
{
/* subtract with overflow check */
register long r;
r = a - b;
*overflow = suboverflow(a, b, r);
return r;
}
#endif
#ifndef LONG_MUL
long long_mul(long a, long b, int *overflow) /*;long_mul*/
{
/* multiply with overflow check */
register long r;
if(a) {
r = a * b;
*overflow = (b != r/a) || (a == -1 && b < 0 && r < 0);
}
else {
r = 0;
*overflow = (int)r;
}
return r;
}
#endif
#ifndef MOVE_MEM
void move_mem(int *src, int *dst, int n) /*;move_mem*/
{
/* move n words from src to dst
* We must watch for possible overlap.
*/
unsigned long usrc, udst;
unsigned int i;
/* View pointers as unsigned to see if possible overlap */
if (n==0) return;
usrc = (unsigned) src;
udst = (unsigned) dst;
if (usrc >= udst) { /* if no possibility of overlap */
for (i=0;i<n;i++)
*dst++ = *src++;
}
else {
/* Here if possible overlap (usrc<udst) , set base to smaller
* of pointer values and determine corresponding indices
*/
if ((usrc + sizeof(int)*(n-1)) < udst ) { /* can use upwards loops */
for (i=0; i<n; i++)
*dst++ = *src++;
}
else { /* overlap, must move backwards */
;
n--;
dst += n;
src += n;
for (i=0; i<=n; i++) {
*dst-- = *src--;
}
}
}
}
#endif
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