C 语言实现的将 Double 转成二进制

getBinary.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>


typedef struct Binary {
  char sign;
  char exp[12];
  char precision[53];
} Binary;


// For transform the double to binary 
Binary *dtob(double a) {
  long num = *(long *)&a;

  const int len = 64;
  char binary[len + 1];
  binary[64] = '\0';
  for (int i = 0; i < len; ++i) {
    binary[i] = (num & 1L) + '0';
    num >>= 1;
  }


  Binary *bin = (Binary *)malloc(sizeof(Binary));
  
  // 首尾交换，因为是小端
  int i = 0, j = len - 1;
  while (i < j) {
    char temp = binary[i];
    binary[i] = binary[j];
    binary[j] = temp;

    i += 1;
    j -= 1;
  }

  bin->sign = binary[0];
  strncpy(bin->exp, binary + 1, 11);
  strcpy(bin->precision, binary + 12);
  return bin;
}

void getBinary(Binary *bin) {
  printf("Sign: %c\n", bin->sign);
  printf("Exp: %s\n", bin->exp);
  printf("Precision: %s\n", bin->precision);
  free(bin);
}

const double charToDouble(char *s) {
  double left = 0;
  double right = 0;

  
  while (*s) {
    if (*s >= '0' && *s <= '9') {
      left = left * 10 + *s - '0';
    }
    if (*s == '.') {
      s++;
      break;
    }
    s++;
  }

  double base = 10.0;
  while (*s) {
    if (*s >= '0' && *s <= '9') {
      right += (*s - '0') / base;
      base *= 10;
    }
    s++;
  }

  return left + right;
}


void output(double f) {
  printf("浮点数 %lf: \n", f);
  getBinary(dtob(f));
  puts("");
}

double create-nan() {
  unsigned char *bits = calloc(sizeof(double), 1);
  // 大部分人的电脑是小端，所以要从 6 和 7 开始，而不是 0 和 1
  // 不清楚概念的可以参考阮老师：	
  // [理解字节序 - 阮一峰的网络日志](http://www.ruanyifeng.com/blog/2016/11/byte-order.html)
  bits[6] = 255;
  bits[7] = 255;

  unsigned char *start = bits;

  double nan = *(double *)(bits);
  output(nan);
  free(bits);
  return nan;
}

int main (int args, char **argv) {

  const double nan = sqrt(-2);
  const double inf = 1.0 / 0;
  const double ninf = -1.0 / 0;

  while (*++argv) {
    output(charToDouble(*argv));
  }

  output(nan);
  output(inf);
  output(ninf);
  create-nan();

}