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bitrev2.c
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bitrev2.c
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#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <assert.h>
#include <omp.h>
static const unsigned char BRT[] = { /*BitRevertTable256*/
0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF,
};
char *itob(int n)
{
int i, j;
static char buf[64] = {};
for (i = 31, j = 0; i >= 0; i--)
buf[j++] = (n & (1 << i))? '1': '0';
buf[j] = 0;
return buf;
}
int bitrev1(register int n)
{
n = (n & 0xaaaaaaaa) >> 1 | (n & 0x55555555) << 1;
n = (n & 0xcccccccc) >> 2 | (n & 0x33333333) << 2;
n = (n & 0xf0f0f0f0) >> 4 | (n & 0x0f0f0f0f) << 4;
n = (n & 0xff00ff00) >> 8 | (n & 0x00ff00ff) << 8;
n = (n >> 16) | (n << 16);
return n;
}
int bitrev2(int n)
{
int m = BRT[n & 0xff] << 24 |
BRT[(n >> 8) & 0xff] << 16 |
BRT[(n >> 16) & 0xff] << 8 |
BRT[(n >> 24)];
return m;
}
int bitrev3(int n)
{
int m;
unsigned char *p = (unsigned char *)&n;
unsigned char *q = (unsigned char *)&m;
q[3] = BRT[p[0]];
q[2] = BRT[p[1]];
q[1] = BRT[p[2]];
q[0] = BRT[p[3]];
return m;
}
int main(int argc, char *argv[])
{
int i;
volatile int n;
double s, e;
#define DIM 100000000
int *v = malloc(DIM*sizeof(int));
assert(v);
for (i = 0; i < DIM; i++) v[i] = rand();
s = omp_get_wtime();
for (i = 0; i < DIM; i++) {
n = v[i];
n = bitrev1(n);
}
e = omp_get_wtime();
printf ("%f sec\n", e-s);
fflush(stdout);
s = omp_get_wtime();
for (i = 0; i < DIM; i++) {
n = v[i];
n = bitrev2(n);
}
e = omp_get_wtime();
printf ("%f sec\n", e-s);
fflush(stdout);
s = omp_get_wtime();
for (i = 0; i < DIM; i++) {
n = v[i];
n = bitrev3(n);
}
e = omp_get_wtime();
printf ("%f sec\n", e-s);
fflush(stdout);
free(v);
return 0;
}