如何获取浮点数的符号、尾数和指数 [英] How to get the sign, mantissa and exponent of a floating point number

问题描述

我有一个程序，它在两个处理器上运行，其中一个不支持浮点.因此，我需要在该处理器中使用定点执行浮点计算.为此，我将使用浮点仿真库.

我需要首先在支持浮点的处理器上提取浮点数的符号、尾数和指数.所以，我的问题是如何获得单精度浮点数的符号、尾数和指数.

按照该图的格式，

这就是我到目前为止所做的，但除了符号，尾数和指数都不正确.我想，我错过了一些东西.

void getSME(int&s,int&m,int&e,浮点数){unsigned int* ptr = (unsigned int*)&number;s = *ptr >>31;e = *ptr &0x7f800000;e>>= 23；m = *ptr &0x007fffff;}

解决方案

我觉得用联合来做强制转换比较好，更清晰.

#include <stdio.h>typedef联合{浮动 f;结构{无符号整数尾数:23；无符号整数指数:8；无符号整数符号:1；} 部分;} float_cast;诠释主要(无效){float_cast d1 = { .f = 0.15625 };printf("sign = %x
", d1.parts.sign);printf("指数 = %x
", d1.parts.exponent);printf("mantisa = %x
", d1.parts.mantisa);}

示例基于 http://en.wikipedia.org/wiki/Single_precisionp>

I have a program, which is running on two processors, one of which does not have floating point support. So, I need to perform floating point calculations using fixed point in that processor. For that purpose, I will be using a floating point emulation library.

I need to first extract the signs, mantissas and exponents of floating point numbers on the processor which do support floating point. So, my question is how can I get the sign, mantissa and exponent of a single precision floating point number.

Following the format from this figure,

That is what I've done so far, but except sign, neither mantissa and exponent are correct. I think, I'm missing something.

void getSME( int& s, int& m, int& e, float number )
{
    unsigned int* ptr = (unsigned int*)&number;

    s = *ptr >> 31;
    e = *ptr & 0x7f800000;
    e >>= 23;
    m = *ptr & 0x007fffff;
}

解决方案

I think it is better to use unions to do the casts, it is clearer.

#include <stdio.h>

typedef union {
  float f;
  struct {
    unsigned int mantisa : 23;
    unsigned int exponent : 8;
    unsigned int sign : 1;
  } parts;
} float_cast;

int main(void) {
  float_cast d1 = { .f = 0.15625 };
  printf("sign = %x
", d1.parts.sign);
  printf("exponent = %x
", d1.parts.exponent);
  printf("mantisa = %x
", d1.parts.mantisa);
}

Example based on http://en.wikipedia.org/wiki/Single_precision

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