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Full Discussion: restricted pointers
Top Forums Programming restricted pointers Post 302171876 by carl.alv on Friday 29th of February 2008 10:34:22 PM
Old 02-29-2008
restricted pointers
Hi all. I am trying to use restricted pointers to allow the gcc compiler optimize the code, but I have not been able to make it work so far. I am testing with this code:

Code:
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <sys/time.h>

void vecmult(int n, int * restrict a, int * restrict b, int * restrict c)
{
  int i;
  for (i=0; i<n; ++i) {
    a[i] = b[i] * c[i];
  }
}

int main(){
  int Nsteps = 100000;
  int n = 1000;
  int* a=NULL; 
  int* b=NULL;
  int* c=NULL;

  //allocate memory
  a = malloc(n*sizeof(int));
  b = malloc(n*sizeof(int));
  c = malloc(n*sizeof(int));

  //initialize arrays
  for(int i = 0; i < n; ++i){
    a[i] = i;
    b[i] = 1;
    c[i] = 0;
  }

  //initialize time
  struct timeval tim;
  gettimeofday(&tim, NULL);
  long tcpu = clock();

  for(int i = 0; i < Nsteps; ++i){
    vecmult(n, a, b, c);
  }

  //time difference evaluation
  double t1 = tim.tv_sec + tim.tv_usec / 1000000.0;
  double start = (double)(tcpu);
  gettimeofday(&tim, NULL);
  double t2 = tim.tv_sec + tim.tv_usec / 1000000.0;
  tcpu = clock();
  double stop = (double)(tcpu);
  double t_elap = (t2 - t1);
  double t_cpu = (stop - start) / 1000000.0;
  //print
  printf("%f %f\n",t_elap, t_cpu);

  //deallocate memory
  free(a);
  free(b);
  free(c);

  //show that restrict does not work
  int l = 1;
  int* restrict p1=NULL;
  int* restrict p2=NULL;
  p1 = &l;
  p2 = p1;

  return 0;
}

The gcc-4.2 compiler does not even complaints for the last part with the -O3 and -std=c99 options. Dues someone knows how to make restricted pointers work? Thanks in advance.
 

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LEARN ABOUT MOJAVE

fxprintf

XPRINTF(3)						   BSD Library Functions Manual 						XPRINTF(3)

NAME

     asxprintf, dxprintf, fxprintf, sxprintf, xprintf, vasxprintf, vdxprintf, vfxprintf, vsxprintf, vxprintf -- extensible printf

SYNOPSIS

     #include <printf.h>

     int
     asxprintf(char ** restrict ret, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, ...);

     int
     dxprintf(int fd, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, ...);

     int
     fxprintf(FILE * restrict stream, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, ...);

     int
     sxprintf(char * restrict str, size_t size, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, ...);

     int
     xprintf(printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, ...);

     #include <stdarg.h>

     int
     vasxprintf(char ** restrict ret, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, va_list ap);

     int
     vdxprintf(int fd, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, va_list ap);

     int
     vfxprintf(FILE * restrict stream, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, va_list ap);

     int
     vsxprintf(char * restrict str, size_t size, printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format,
	 va_list ap);

     int
     vxprintf(printf_domain_t restrict domain, locale_t restrict loc, const char * restrict format, va_list ap);

DESCRIPTION

     These extensible printf (see xprintf(5)) variants behave like their normal printf counterparts (see printf(3)) without 'x' in the name
     (except sxprintf() and vsxprintf() behave like snprintf() and vsnprintf(), respectively).

     The domain argument must be a pointer to a printf domain structure, as returned by one of the functions described in xprintf_domain(3).  The
     loc argument should be an extended locale (see xlocale(3)) or NULL, which means to use the current locale in effect (either the per-thread
     locale if set, or the global locale by default).

SEE ALSO

     printf(3), xlocale(3), xprintf_domain(3), xprintf(5)

Darwin								   Aug 19, 2012 							    Darwin
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