diff options
Diffstat (limited to 'Objects')
| -rw-r--r-- | Objects/floatobject.c | 184 |
1 files changed, 183 insertions, 1 deletions
diff --git a/Objects/floatobject.c b/Objects/floatobject.c index da600f4..0642b16 100644 --- a/Objects/floatobject.c +++ b/Objects/floatobject.c @@ -1975,8 +1975,120 @@ _PyFloat_DebugMallocStats(FILE *out) /*---------------------------------------------------------------------------- - * _PyFloat_{Pack,Unpack}{4,8}. See floatobject.h. + * _PyFloat_{Pack,Unpack}{2,4,8}. See floatobject.h. + * To match the NPY_HALF_ROUND_TIES_TO_EVEN behavior in: + * https://github.com/numpy/numpy/blob/master/numpy/core/src/npymath/halffloat.c + * We use: + * bits = (unsigned short)f; Note the truncation + * if ((f - bits > 0.5) || (f - bits == 0.5 && bits % 2)) { + * bits++; + * } */ + +int +_PyFloat_Pack2(double x, unsigned char *p, int le) +{ + unsigned char sign; + int e; + double f; + unsigned short bits; + int incr = 1; + + if (x == 0.0) { + sign = (copysign(1.0, x) == -1.0); + e = 0; + bits = 0; + } + else if (Py_IS_INFINITY(x)) { + sign = (x < 0.0); + e = 0x1f; + bits = 0; + } + else if (Py_IS_NAN(x)) { + /* There are 2046 distinct half-precision NaNs (1022 signaling and + 1024 quiet), but there are only two quiet NaNs that don't arise by + quieting a signaling NaN; we get those by setting the topmost bit + of the fraction field and clearing all other fraction bits. We + choose the one with the appropriate sign. */ + sign = (copysign(1.0, x) == -1.0); + e = 0x1f; + bits = 512; + } + else { + sign = (x < 0.0); + if (sign) { + x = -x; + } + + f = frexp(x, &e); + if (f < 0.5 || f >= 1.0) { + PyErr_SetString(PyExc_SystemError, + "frexp() result out of range"); + return -1; + } + + /* Normalize f to be in the range [1.0, 2.0) */ + f *= 2.0; + e--; + + if (e >= 16) { + goto Overflow; + } + else if (e < -25) { + /* |x| < 2**-25. Underflow to zero. */ + f = 0.0; + e = 0; + } + else if (e < -14) { + /* |x| < 2**-14. Gradual underflow */ + f = ldexp(f, 14 + e); + e = 0; + } + else /* if (!(e == 0 && f == 0.0)) */ { + e += 15; + f -= 1.0; /* Get rid of leading 1 */ + } + + f *= 1024.0; /* 2**10 */ + /* Round to even */ + bits = (unsigned short)f; /* Note the truncation */ + assert(bits < 1024); + assert(e < 31); + if ((f - bits > 0.5) || ((f - bits == 0.5) && (bits % 2 == 1))) { + ++bits; + if (bits == 1024) { + /* The carry propagated out of a string of 10 1 bits. */ + bits = 0; + ++e; + if (e == 31) + goto Overflow; + } + } + } + + bits |= (e << 10) | (sign << 15); + + /* Write out result. */ + if (le) { + p += 1; + incr = -1; + } + + /* First byte */ + *p = (unsigned char)((bits >> 8) & 0xFF); + p += incr; + + /* Second byte */ + *p = (unsigned char)(bits & 0xFF); + + return 0; + + Overflow: + PyErr_SetString(PyExc_OverflowError, + "float too large to pack with e format"); + return -1; +} + int _PyFloat_Pack4(double x, unsigned char *p, int le) { @@ -2212,6 +2324,76 @@ _PyFloat_Pack8(double x, unsigned char *p, int le) } double +_PyFloat_Unpack2(const unsigned char *p, int le) +{ + unsigned char sign; + int e; + unsigned int f; + double x; + int incr = 1; + + if (le) { + p += 1; + incr = -1; + } + + /* First byte */ + sign = (*p >> 7) & 1; + e = (*p & 0x7C) >> 2; + f = (*p & 0x03) << 8; + p += incr; + + /* Second byte */ + f |= *p; + + if (e == 0x1f) { +#ifdef PY_NO_SHORT_FLOAT_REPR + if (f == 0) { + /* Infinity */ + return sign ? -Py_HUGE_VAL : Py_HUGE_VAL; + } + else { + /* NaN */ +#ifdef Py_NAN + return sign ? -Py_NAN : Py_NAN; +#else + PyErr_SetString( + PyExc_ValueError, + "can't unpack IEEE 754 NaN " + "on platform that does not support NaNs"); + return -1; +#endif /* #ifdef Py_NAN */ + } +#else + if (f == 0) { + /* Infinity */ + return _Py_dg_infinity(sign); + } + else { + /* NaN */ + return _Py_dg_stdnan(sign); + } +#endif /* #ifdef PY_NO_SHORT_FLOAT_REPR */ + } + + x = (double)f / 1024.0; + + if (e == 0) { + e = -14; + } + else { + x += 1.0; + e -= 15; + } + x = ldexp(x, e); + + if (sign) + x = -x; + + return x; +} + +double _PyFloat_Unpack4(const unsigned char *p, int le) { if (float_format == unknown_format) { |