modernc.org/ccgo/v3@v3.16.14/lib/testdata/CompCert-3.6/test/c/spectral.c (about)

     1  /* -*- mode: c -*-
     2   *
     3   * The Great Computer Language Shootout
     4   * http://shootout.alioth.debian.org/
     5   *
     6   * Contributed by Sebastien Loisel
     7   */
     8  
     9  #include <stdio.h>
    10  #include <stdlib.h>
    11  #include <math.h>
    12  
    13  static inline double eval_A(int i, int j) { return 1.0/((i+j)*(i+j+1)/2+i+1); }
    14  
    15  void eval_A_times_u(int N, const double u[], double Au[])
    16  {
    17    int i,j;
    18    for(i=0;i<N;i++)
    19      {
    20        Au[i]=0;
    21        for(j=0;j<N;j++) Au[i]+=eval_A(i,j)*u[j];
    22      }
    23  }
    24  
    25  void eval_At_times_u(int N, const double u[], double Au[])
    26  {
    27    int i,j;
    28    for(i=0;i<N;i++)
    29      {
    30        Au[i]=0;
    31        for(j=0;j<N;j++) Au[i]+=eval_A(j,i)*u[j];
    32      }
    33  }
    34  
    35  void eval_AtA_times_u(int N, const double u[], double AtAu[])
    36  {
    37    double *v = malloc(N * sizeof(double));
    38    eval_A_times_u(N,u,v);
    39    eval_At_times_u(N,v,AtAu);
    40    free(v);
    41  }
    42  
    43  int main(int argc, char *argv[])
    44  {
    45    int i;
    46    int N = ((argc == 2) ? atoi(argv[1]) : 1000);
    47    double * u, * v, vBv, vv;
    48    u = malloc(N * sizeof(double));
    49    v = malloc(N * sizeof(double));
    50    for(i=0;i<N;i++) u[i]=1;
    51    for(i=0;i<10;i++)
    52      {
    53        eval_AtA_times_u(N,u,v);
    54        eval_AtA_times_u(N,v,u);
    55      }
    56    vBv=vv=0;
    57    for(i=0;i<N;i++) { vBv+=u[i]*v[i]; vv+=v[i]*v[i]; }
    58    printf("%0.9f\n",sqrt(vBv/vv));
    59    return 0;
    60  }
    61  
    62  /********
    63   build & benchmark results
    64  
    65  BUILD COMMANDS FOR: spectralnorm.gcc
    66  
    67  Fri Sep 15 20:48:08 PDT 2006
    68  
    69  /usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -funroll-loops -march=pentium4 -lm spectralnorm.c -o spectralnorm.gcc_run
    70  
    71  =================================================================
    72  COMMAND LINE (%A is single numeric argument):
    73  
    74  spectralnorm.gcc_run %A
    75  
    76  N=2500
    77  
    78  PROGRAM OUTPUT
    79  ==============
    80  1.274224153
    81  ********/