C语言索引遍历探究#

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# include "alloc_function.h"
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# include <stdio.h>
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# include <stdlib.h>
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# include <string.h>
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#include <limits.h>
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# define TIMES 21
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int main()
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{
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    clock_t t0, t1, t2;
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    float *arr1d;
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    float ***arr3d;
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    float time_r;
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    float sum;
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    float *pointer;
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    size_t N1=2000;
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    size_t N2=1000;
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    size_t N3=50;
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    arr1d = alloc1float(N1*N2*N3);
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    arr3d = alloc3float(N1,N2,N3);
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    size_t N = N1*N2*N3;
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    printf("N=%ld\n", N);
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    printf("size_t=[0,%u]\n", UINT_MAX);
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    printf("int   =[%d,%d]\n", INT_MIN, INT_MAX);
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    // 1D array
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    time_r=0.0f;
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    for(size_t time=0; time<TIMES; time++){
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        t0 = clock();
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        sum = 0.0f;
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        for(size_t i=0; i<N; i++)
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        {
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            arr1d[i] = 1e-6f;
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            sum += arr1d[i];
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        }
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        t1 = clock();
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        if (time>0)
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        time_r += (float)(t1-t0)/1000000.0;
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    }
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    printf("1D array: %f \t %f\n", time_r,sum);
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    // 1D array pointer
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    time_r=0.0f;
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    for(size_t time=0; time<TIMES; time++){
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        t0 = clock();
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        sum = 0.0f;
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        for(pointer = arr1d; pointer<arr1d+N; pointer++)
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        {
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            *pointer = 1e-6f;
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            sum += *pointer;
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        }
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        t1 = clock();
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        if (time>0)
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        time_r += (float)(t1-t0)/1000000.0;
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    }
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    printf("1D array pointer: %f \t %f \n", time_r, sum);
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    // 3D array Nonequential read
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    time_r=0.0f;
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    for(size_t time=0; time<TIMES; time++){
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        t0 = clock();
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        sum = 0.0f;
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        for(size_t i=0; i<N1; i++)
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        {
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            for(size_t j=0; j<N2; j++)
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            {
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                for(size_t k=0; k<N3; k++){
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                    arr3d[k][j][i] = 1e-6f;
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                    sum += arr3d[k][j][i];
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                }
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            }
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        }
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        t1 = clock();
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        if (time>0)
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        time_r += (float)(t1-t0)/1000000.0;
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    }
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    printf("3D array Nonequential: %f \t %f\n", time_r, sum);
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    // 3D array Sequential read
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    time_r=0.0f;
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    for(size_t time=0; time<TIMES; time++){
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        t0 = clock();
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        sum = 0.0f;
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        for(size_t k=0; k<N3; k++)
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        {
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            for(size_t j=0; j<N2; j++)
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            {
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                for(size_t i=0; i<N1; i++){
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                    arr3d[k][j][i] = 1e-6f;
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                    sum += arr3d[k][j][i];
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                }
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            }
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        }
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        t1 = clock();
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        if (time>0)
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        time_r += (float)(t1-t0)/1000000.0;
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    }
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     printf("3D array Sequential: %f \t %f\n", time_r, sum);
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}