| 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 | |
| 10 | uint64_t pack754(long double f, unsigned bits, unsigned expbits) |
| 11 | { |
| 12 | long double fnorm; |
| 13 | int shift; |
| 14 | long long sign, exp, significand; |
| 15 | unsigned significandbits = bits - expbits - 1; // -1 for sign bit |
| 16 | |
| 17 | // get this special case out of the way |
| 18 | if (f == 0.0) |
| 19 | return 0; |
| 20 | |
| 21 | // check sign and begin normalization |
| 22 | if (f < 0) { |
| 23 | sign = 1; |
| 24 | fnorm = -f; |
| 25 | } else { |
| 26 | sign = 0; |
| 27 | fnorm = f; |
| 28 | } |
| 29 | |
| 30 | // get the normalized form of f and track the exponent |
| 31 | shift = 0; |
| 32 | while (fnorm >= 2.0) { |
| 33 | fnorm /= 2.0; |
| 34 | shift++; |
| 35 | } |
| 36 | while (fnorm < 1.0) { |
| 37 | fnorm *= 2.0; |
| 38 | shift--; |
| 39 | } |
| 40 | fnorm = fnorm - 1.0; |
| 41 | |
| 42 | // calculate the binary form (non-float) of the significand data |
| 43 | significand = fnorm * ((1LL << significandbits) + 0.5f); |
| 44 | |
| 45 | // get the biased exponent |
| 46 | exp = shift + ((1 << (expbits - 1)) - 1); // shift + bias |
| 47 | |
| 48 | // return the final answer |
| 49 | return (sign << (bits - 1)) | (exp << (bits-expbits - 1)) | significand; |
| 50 | } |
| 51 | |
| 52 | long double unpack754(uint64_t i, unsigned bits, unsigned expbits) |
| 53 | { |
| 54 | long double result; |
| 55 | long long shift; |
| 56 | unsigned bias; |
| 57 | unsigned significandbits = bits - expbits - 1; // -1 for sign bit |
| 58 | |
| 59 | if (i == 0) |
| 60 | return 0.0; |
| 61 | |
| 62 | // pull the significand |
| 63 | result = (i & ((1LL << significandbits) - 1)); // mask |
| 64 | result /= (1LL << significandbits); // convert back to float |
| 65 | result += 1.0f; // add the one back on |
| 66 | |
| 67 | // deal with the exponent |
| 68 | bias = (1 << (expbits - 1)) - 1; |
| 69 | shift = ((i >> significandbits) & ((1LL << expbits) - 1)) - bias; |
| 70 | while (shift > 0) { |
| 71 | result *= 2.0; |
| 72 | shift--; |
| 73 | } |
| 74 | while (shift < 0) { |
| 75 | result /= 2.0; |
| 76 | shift++; |
| 77 | } |
| 78 | |
| 79 | // sign it |
| 80 | result *= (i >> (bits - 1)) & 1 ? -1.0 : 1.0; |
| 81 | |
| 82 | return result; |
| 83 | } |