对20byte数据进行二进制算术编码的c实现

以下是对20byte数据进行二进制算术编码的C语言实现：

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#define MAX_CODE 0xFFFFFFFF

typedef struct {
    uint32_t low;           // 下界
    uint32_t high;          // 上界
    uint32_t code;          // 区间编码
} Range;

void encode(char *data, int len) {
    // 初始化符号概率，这里假设每个符号出现概率相等
    uint32_t freq[256] = {0};
    for (int i = 0; i < len; i++) {
        freq[(unsigned char)data[i]]++;
    }
    uint32_t total = len;
    for (int i = 0; i < 256; i++) {
        if (freq[i] > 0) {
            freq[i] = (freq[i] << 16) / total;
            if (freq[i] == 0) {
                freq[i] = 1;
            }
        }
    }

    Range range = {0, MAX_CODE, 0};      // 初始化区间编码器
    for (int i = 0; i < len; i++) {
        uint32_t symbol = (unsigned char)data[i];
        uint32_t lcode = range.low + freq[symbol] * (range.high - range.low) >> 16;
        uint32_t hcode = range.low + freq[symbol + 1] * (range.high - range.low) >> 16;
        range.low = lcode;
        range.high = hcode;
        // 将区间编码标准化
        while ((range.low ^ range.high) < (1L << 31)) {
            uint32_t bit = range.low >> 31;
            putchar(bit + '0');
            while (range.code > 0) {
                putchar('1' - bit);
                range.code--;
            }
            range.low = (range.low << 1) & MAX_CODE;
            range.high = ((range.high << 1) | 1) & MAX_CODE;
        }
        // 丢弃相同的二进制位
        while (((range.low & 0x80000000) == (range.high & 0x80000000))) {
            uint32_t bit = range.low >> 31;
            putchar(bit + '0');
            while (range.code > 0) {
                putchar('1' - bit);
                range.code--;
            }
            range.low = (range.low << 1) & MAX_CODE;
            range.high = ((range.high << 1) | 1) & MAX_CODE;
        }
    }
    // 输出最后的二进制编码
    uint32_t bit = range.low >> 31;
    putchar(bit + '0');
    while (range.code > 0) {
        putchar('1' - bit);
        range.code--;
    }
}

int main(void) {
    char data[] = "Hello, world! This is binary arithmetic coding.";
    encode(data, sizeof(data));
    return 0;
}

这个程序会将输入的数据编码为一串二进制位，并输出到标准输出中。具体的实现过程可以参考注释。