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82 lines
1.9 KiB
82 lines
1.9 KiB
/*
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* Handling of floating point casts.
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*
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* Little endian only.
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*/
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#include <stdio.h>
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#include <math.h>
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#if 0
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#define __FLT_MAX__ 3.40282346638528859812e+38F
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#endif
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#define FLT_MAX 340282346638528859811704183484516925440.0
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#define FLT_MAX_PLUS 340282366920938463463374607431768211456.0
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static void dump_memory(volatile unsigned char *p, size_t len) {
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size_t i, idx;
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for (i = 0; i < len; i++) {
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idx = len - i - 1; /* for little endian */
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printf("%02x", (unsigned int) p[idx]);
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}
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printf("\n");
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}
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int main(int argc, const char *argv[]) {
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volatile double d;
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volatile float f;
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volatile unsigned char *p;
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/* FLT_MAX: (1 - 2^(-24)) * 2^128. */
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printf("- FLT_MAX\n");
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d = FLT_MAX;
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f = (float) d;
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printf("d: %f\n", d);
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printf("f: %f\n", f);
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dump_memory((volatile unsigned char *) &d, 8);
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dump_memory((volatile unsigned char *) &f, 4);
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/* FLT_MAX + floating point unit: 2^128. */
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printf("- FLT_MAX_PLUS\n");
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d = FLT_MAX_PLUS;
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f = (float) d;
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printf("d: %f\n", d);
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printf("f: %f\n", f);
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dump_memory((volatile unsigned char *) &d, 8);
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dump_memory((volatile unsigned char *) &f, 4);
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/* Number between FLT_MAX and FLT_MAX + unit. */
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printf("- between FLT_MAX and FLT_MAX_PLUS\n");
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d = (FLT_MAX + FLT_MAX_PLUS) / 2.0;
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f = (float) d;
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printf("d: %f\n", d);
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printf("f: %f\n", f);
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dump_memory((volatile unsigned char *) &d, 8);
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dump_memory((volatile unsigned char *) &f, 4);
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/* Same as above, but one double unit less.
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* 47effffff0000000 ->
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* 47efffffefffffff
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*
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* This is the largest double that doesn't round to infinity on x64.
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*/
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printf("- just below above\n");
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p = (volatile unsigned char *) &d;
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p[7] = 0x47U;
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p[6] = 0xefU;
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p[5] = 0xffU;
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p[4] = 0xffU;
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p[3] = 0xefU;
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p[2] = 0xffU;
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p[1] = 0xffU;
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p[0] = 0xffU;
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f = (float) d;
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printf("d: %f\n", d);
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printf("f: %f\n", f);
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dump_memory((volatile unsigned char *) &d, 8);
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dump_memory((volatile unsigned char *) &f, 4);
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return 0;
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}
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