一个压缩小整数的算法zipzag,原文来自这里, http://mp.weixin.qq.com/s?__biz=MzA3MDExNzcyNA==&mid=2650392086&idx=1&sn=6a2ecfe2548f121a4726d03bf23f4478

zipzag.c

//一个压缩小整数的算法,原文来自这里
//http://mp.weixin.qq.com/s?__biz=MzA3MDExNzcyNA==&mid=2650392086&idx=1&sn=6a2ecfe2548f121a4726d03bf23f4478
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>

typedef unsigned char byte;

////http://stackoverflow.com/questions/111928/is-there-a-printf-converter-to-print-in-binary-format?page=1&tab=active#tab-top
//assumes little endian
void printBits(size_t const size, void const *const ptr) {
  unsigned char *b = (unsigned char *) ptr;
  unsigned char byte;
  int i, j;

  for (i = size - 1; i >= 0; i--) {
    for (j = 7; j >= 0; j--) {
      byte = (b[i] >> j) & 1;
      printf("%u", byte);
    }
    if (i > 0) printf("_");
  }
  puts("");
}

int int_to_zipzag(int n) {
  return (n << 1) ^ (n >> 31);
}

int zipzag_to_int(int n) {
  return ((unsigned int) n >> 1) ^ -(n & 1);
}

int write_to_buffer(int zz, byte *buf, int size) {
  int ret = 0;
  for (int i = 0; i < size; i++) {
    if ((zz & (~0x7F)) == 0) {
      buf[i] = (byte) zz;
      ret = i + 1;
      break;
    } else {
      buf[i] = (byte) ((zz & 0x7F) | 0x80);
      zz = (unsigned int) zz >> 7;
    }
  }

  return ret;
}

//我实现方式
int read_from_buffer2(byte *buf, int max_size) {
  int result = 0;     //最后要返回的int型值
  int offset = 0;     //ret需要偏移的位数(即目前是处理第几个 7bit 位)
  for (int i = 0; i < max_size; i++, offset += 7) {
    result |= (buf[i] & 0x7F) << offset;
    if ((buf[i] & 0x80) == 0) break;
  }

  return result;
}

int read_from_buffer(byte *buf, int max_size) {
  int ret = 0;
  int offset = 0;
  for (int i = 0; i < max_size; i++, offset += 7) {
    byte n = buf[i];     //取出一组 7bit 位, 第 8bit 位为符号位,代表是否为最后一组 7bit 位
    if ((n & 0x80) != 0x80) { //第 8bit 位为 0 (表示为最后一组 7bit 位)
      ret |= (n << offset);
      break;
    } else {
      ret |= ((n & 0x7f) << offset);
    }
  }

  return ret;
}

int main() {
  int a[] = {
      (int) (-pow(2L, 32)),
      -1000,
      -10000,
      -1,
      0,
      1,
      1000,
      10000,
      getpid(),
      rand()-10000,
      (int) (pow(2L, 31) - 1L)
  };

  for (int i = 0; i < sizeof(a) / sizeof(int); i++) {
    int n = a[i];
    printf("number: %15d ", n);
    printBits(sizeof(n), &n);

    int zz = int_to_zipzag(n);
    printf("zipnum: %15d ", zz);
    printBits(sizeof(zz), &zz);

    byte write_buffer[5] = {0};
    int write_size = write_to_buffer(zz, write_buffer, sizeof(write_buffer));
    printf("zipbuf: %11dbyte ", write_size);
    printBits(write_size, &write_buffer);

    int read_num = read_from_buffer(write_buffer, write_size);
    printf("re1num: %15d ", read_num);
    printBits(sizeof(read_num), &read_num);

    int read_num2 = read_from_buffer2(write_buffer, sizeof(write_buffer));
    printf("re2num: %15d ", read_num2);
    printBits(sizeof(read_num2), &read_num2);

    int org1_num = zipzag_to_int(read_num);
    printf("numbe1: %15d ", org1_num);
    printBits(sizeof(org1_num), &org1_num);

    int org2_num = zipzag_to_int(read_num2);
    printf("numbe2: %15d ", org2_num);
    printBits(sizeof(org2_num), &org2_num);

    puts("");
  }
}