漫话Redis源码之六十四

这里主要是内存相关的一些操作，C语言爱好者肯定很熟悉。其实也不难。

#include <stdint.h>
 
/* Toggle the 16 bit unsigned integer pointed by *p from little endian to
 * big endian */
void memrev16(void *p) {
    unsigned char *x = p, t;
 
    t = x[0];
    x[0] = x[1];
    x[1] = t;
}
 
/* Toggle the 32 bit unsigned integer pointed by *p from little endian to
 * big endian */
void memrev32(void *p) {
    unsigned char *x = p, t;
 
    t = x[0];
    x[0] = x[3];
    x[3] = t;
    t = x[1];
    x[1] = x[2];
    x[2] = t;
}
 
/* Toggle the 64 bit unsigned integer pointed by *p from little endian to
 * big endian */
void memrev64(void *p) {
    unsigned char *x = p, t;
 
    t = x[0];
    x[0] = x[7];
    x[7] = t;
    t = x[1];
    x[1] = x[6];
    x[6] = t;
    t = x[2];
    x[2] = x[5];
    x[5] = t;
    t = x[3];
    x[3] = x[4];
    x[4] = t;
}
 
uint16_t intrev16(uint16_t v) {
    memrev16(&v);
    return v;
}
 
uint32_t intrev32(uint32_t v) {
    memrev32(&v);
    return v;
}
 
uint64_t intrev64(uint64_t v) {
    memrev64(&v);
    return v;
}
 
#ifdef REDIS_TEST
#include <stdio.h>
 
#define UNUSED(x) (void)(x)
int endianconvTest(int argc, char *argv[], int accurate) {
    char buf[32];
 
    UNUSED(argc);
    UNUSED(argv);
    UNUSED(accurate);
 
    sprintf(buf,"ciaoroma");
    memrev16(buf);
    printf("%s\n", buf);
 
    sprintf(buf,"ciaoroma");
    memrev32(buf);
    printf("%s\n", buf);
 
    sprintf(buf,"ciaoroma");
    memrev64(buf);
    printf("%s\n", buf);
 
    return 0;
}
#endif