C－确定char、short、int、long、long long、float和double的范围

Myth丶恋晨 2022-12-31 12:26 160阅读 0赞

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/*
     * Range.c - by FreeMan
     */
    
    #include <stdio.h>
    #include <limits.h>
    
    float GetFloat(char sign, unsigned char exp, unsigned mantissa);
    double GetDouble(char sign, unsigned short exp, unsigned long long mantissa);
    
    int main(void)
    {
    	printf("Signed char [%d to %d]\n", 
    		~((unsigned char)~0 >> 1), (unsigned char)~0 >> 1);
    	printf("Unsigned char [0 to %u]\n", (unsigned char)~0);
    
    	printf("Signed short [%d to %d]\n", 
    		~((unsigned short)~0 >> 1), (unsigned short)~0 >> 1);
    	printf("Unsigned short [0 to %u]\n", (unsigned short)~0);
    
    	printf("Signed int [%d to %d]\n", ~(~0U >> 1), ~0U >> 1);
    	printf("Unsigned int [0 to %u]\n", ~0U);
    
    	printf("Signed long [%ld to %ld]\n", ~(~0UL >> 1), ~0UL >> 1);
    	printf("Unsigned long [0 to %lu]\n", ~0UL);
    
    	printf("Signed long long [%lld to %lld]\n", ~(~0ULL >> 1), ~0ULL >> 1);
    	printf("Unsigned long long [0 to %llu]\n", ~0ULL);
    
    	printf("Float [%g to %g]\n", GetFloat(1, 0, 1), GetFloat(0, ~0 - 1, ~0));
    
    	printf("Double [%g to %g]\n", GetDouble(1, 0, 1), GetDouble(0, ~0 - 1, ~0));
    
    	return 0;
    }
    
    float GetFloat(char sign, unsigned char exp, unsigned mantissa)
    {
    	unsigned f = (unsigned)(sign != 0) << 31 | (unsigned)exp << 23 
    		| mantissa & 0x7FFFFF;
    	return *((float *)&f);
    }
    
    double GetDouble(char sign, unsigned short exp, unsigned long long mantissa)
    {
    	unsigned long long d = (unsigned long long)(sign != 0) << 63 
    		| (unsigned long long)(exp & 0x7FF) << 52 | mantissa & 0xFFFFFFFFFFFFF;
    	return *((double *)&d);
    }
    
    // Output:
    /*
    Signed char [-128 to 127]
    Unsigned char [0 to 255]
    Signed short [-32768 to 32767]
    Unsigned short [0 to 65535]
    Signed int [-2147483648 to 2147483647]
    Unsigned int [0 to 4294967295]
    Signed long [-2147483648 to 2147483647]
    Unsigned long [0 to 4294967295]
    Signed long long [-9223372036854775808 to 9223372036854775807]
    Unsigned long long [0 to 18446744073709551615]
    Float [-1.4013e-45 to 3.40282e+38]
    Double [-4.94066e-324 to 1.79769e+308]
    
    */

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