csapp2e를 보다가 작성해서 테스트 해 본 코드.
math.h에 NAN은0x7fc00000 로 정의되어 있다. 그러나 이 floating point 밸류를 NAN과 비교해 판별하면 무조건 다르게 나온다는 점. NaN을 판별하려면 isnan() 함수를 사용하거나, exponent bits를 봐야 할 듯.
//
// main.c
// floatingpoint_bits
//
// Created by Seong-Su Kim on 2015. 3. 9..
// Copyright (c) 2015년 Seong-Su Kim. All rights reserved.
//
#include <stdio.h>
#include <math.h>
void printfpValue(float fvalue);
void printbitsValue(unsigned bits);
void isNaN(unsigned bits);
int main(void)
{
unsigned long count;
unsigned long start, end;
printf("\n# predefined values\n\n");
printfpValue(NAN);
printfpValue(INFINITY);
if (NAN == NAN)
printf("NAN == NAN!\n"); // will be never executed
printf("\n\n# user bits to floating point value\n\n");
printbitsValue(0xff800000); isNaN(0xff800000);
printbitsValue(0x7f800001); isNaN(0x7f800001);
printbitsValue(0x7fc00000); isNaN(0x7fc00000);
printbitsValue(0xff800001); isNaN(0xff800001);
printf("enter start value : ");
scanf("%lx", &start);
printf("start value = %#lx\n", start);
printf("enter end value : ");
scanf("%lx", &end);
printf("end value = %#lx\n", start);
for (count = start; count <= end; count++)
printbitsValue((unsigned)count);
return 0;
}
void printfpValue(float fvalue)
{
unsigned *bp;
bp = (unsigned *)(&fvalue);
printf("%0#10x = %12e\n", *bp, fvalue);
}
void printbitsValue(unsigned bits)
{
float *fp;
fp = (float *)(&bits);
printf("%0#10x = %12e\n", bits, *fp);
}
void isNaN(unsigned bits)
{
float *fp;
fp = (float *)(&bits);
if (*fp == NAN)
printf("%e == NAN,\t", *fp);
else
printf("%e != NAN,\t", *fp);
if (isnan(*fp))
printf("isnan() says it is NaN.\n\n");
else
printf("isnan() says it is not NaN.\n\n");
}
