1 /*
2 * Shamelessly lifted from Beej's Guide to Network Programming, found here:
3 *
4 * http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html#serialization
5 *
6 * Below code was granted to the public domain.
7 */
8 #include <inttypes.h>
9 #include "ieee754.h"
10
pack754(long double f,unsigned bits,unsigned expbits)11 uint64_t pack754(long double f, unsigned bits, unsigned expbits)
12 {
13 long double fnorm;
14 int shift;
15 long long sign, exp, significand;
16 unsigned significandbits = bits - expbits - 1; // -1 for sign bit
17
18 // get this special case out of the way
19 if (f == 0.0)
20 return 0;
21
22 // check sign and begin normalization
23 if (f < 0) {
24 sign = 1;
25 fnorm = -f;
26 } else {
27 sign = 0;
28 fnorm = f;
29 }
30
31 // get the normalized form of f and track the exponent
32 shift = 0;
33 while (fnorm >= 2.0) {
34 fnorm /= 2.0;
35 shift++;
36 }
37 while (fnorm < 1.0) {
38 fnorm *= 2.0;
39 shift--;
40 }
41 fnorm = fnorm - 1.0;
42
43 // calculate the binary form (non-float) of the significand data
44 significand = fnorm * ((1LL << significandbits) + 0.5f);
45
46 // get the biased exponent
47 exp = shift + ((1 << (expbits - 1)) - 1); // shift + bias
48
49 // return the final answer
50 return (sign << (bits - 1)) | (exp << (bits-expbits - 1)) | significand;
51 }
52
unpack754(uint64_t i,unsigned bits,unsigned expbits)53 long double unpack754(uint64_t i, unsigned bits, unsigned expbits)
54 {
55 long double result;
56 long long shift;
57 unsigned bias;
58 unsigned significandbits = bits - expbits - 1; // -1 for sign bit
59
60 if (i == 0)
61 return 0.0;
62
63 // pull the significand
64 result = (i & ((1LL << significandbits) - 1)); // mask
65 result /= (1LL << significandbits); // convert back to float
66 result += 1.0f; // add the one back on
67
68 // deal with the exponent
69 bias = (1 << (expbits - 1)) - 1;
70 shift = ((i >> significandbits) & ((1LL << expbits) - 1)) - bias;
71 while (shift > 0) {
72 result *= 2.0;
73 shift--;
74 }
75 while (shift < 0) {
76 result /= 2.0;
77 shift++;
78 }
79
80 // sign it
81 result *= (i >> (bits - 1)) & 1 ? -1.0 : 1.0;
82
83 return result;
84 }
85