bundled fpconst-0.7.2

fpconst.py

@@ -0,0 +1,178 @@
+"""Utilities for handling IEEE 754 floating point special values
+
+This python module implements constants and functions for working with
+IEEE754 double-precision special values.  It provides constants for
+Not-a-Number (NaN), Positive Infinity (PosInf), and Negative Infinity
+(NegInf), as well as functions to test for these values.
+
+The code is implemented in pure python by taking advantage of the
+'struct' standard module. Care has been taken to generate proper
+results on both big-endian and little-endian machines. Some efficiency
+could be gained by translating the core routines into C.
+
+See <http://babbage.cs.qc.edu/courses/cs341/IEEE-754references.html>
+for reference material on the IEEE 754 floating point standard.
+
+Further information on this package is available at
+<http://www.analytics.washington.edu/statcomp/projects/rzope/fpconst/>.
+
+------------------------------------------------------------------
+Author:    Gregory R. Warnes <Gregory.R.Warnes@Pfizer.com>
+Date:      2005-02-24
+Version:   0.7.2
+Copyright: (c) 2003-2005 Pfizer, Licensed to PSF under a Contributor Agreement
+License:   Licensed under the Apache License, Version 2.0 (the"License");
+	   you may not use this file except in compliance with the License.
+	   You may obtain a copy of the License at
+
+	       http://www.apache.org/licenses/LICENSE-2.0
+
+	   Unless required by applicable law or agreed to in
+	   writing, software distributed under the License is
+	   distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+	   CONDITIONS OF ANY KIND, either express or implied.  See
+	   the License for the specific language governing
+	   permissions and limitations under the License.
+------------------------------------------------------------------
+"""
+
+__version__ = "0.7.2"
+ident = "$Id: fpconst.py,v 1.16 2005/02/24 17:42:03 warnes Exp $"
+
+import struct, operator
+
+# check endianess
+_big_endian = struct.pack('i',1)[0] != '\x01'
+
+# and define appropriate constants
+if(_big_endian): 
+    NaN    = struct.unpack('d', '\x7F\xF8\x00\x00\x00\x00\x00\x00')[0]
+    PosInf = struct.unpack('d', '\x7F\xF0\x00\x00\x00\x00\x00\x00')[0]
+    NegInf = -PosInf
+else:
+    NaN    = struct.unpack('d', '\x00\x00\x00\x00\x00\x00\xf8\xff')[0]
+    PosInf = struct.unpack('d', '\x00\x00\x00\x00\x00\x00\xf0\x7f')[0]
+    NegInf = -PosInf
+
+def _double_as_bytes(dval):
+    "Use struct.unpack to decode a double precision float into eight bytes"
+    tmp = list(struct.unpack('8B',struct.pack('d', dval)))
+    if not _big_endian:
+        tmp.reverse()
+    return tmp
+
+##
+## Functions to extract components of the IEEE 754 floating point format
+##
+
+def _sign(dval):
+    "Extract the sign bit from a double-precision floating point value"
+    bb = _double_as_bytes(dval)
+    return bb[0] >> 7 & 0x01
+
+def _exponent(dval):
+    """Extract the exponentent bits from a double-precision floating
+    point value.
+
+    Note that for normalized values, the exponent bits have an offset
+    of 1023. As a consequence, the actual exponentent is obtained
+    by subtracting 1023 from the value returned by this function
+    """
+    bb = _double_as_bytes(dval)
+    return (bb[0] << 4 | bb[1] >> 4) & 0x7ff
+
+def _mantissa(dval):
+    """Extract the _mantissa bits from a double-precision floating
+    point value."""
+
+    bb = _double_as_bytes(dval)
+    mantissa =  bb[1] & 0x0f << 48
+    mantissa += bb[2] << 40
+    mantissa += bb[3] << 32
+    mantissa += bb[4]
+    return mantissa 
+
+def _zero_mantissa(dval):
+    """Determine whether the mantissa bits of the given double are all
+    zero."""
+    bb = _double_as_bytes(dval)
+    return ((bb[1] & 0x0f) | reduce(operator.or_, bb[2:])) == 0
+
+##
+## Functions to test for IEEE 754 special values
+##
+
+def isNaN(value):
+    "Determine if the argument is a IEEE 754 NaN (Not a Number) value."
+    return (_exponent(value)==0x7ff and not _zero_mantissa(value))
+
+def isInf(value):
+    """Determine if the argument is an infinite IEEE 754 value (positive
+    or negative inifinity)"""
+    return (_exponent(value)==0x7ff and _zero_mantissa(value))
+
+def isFinite(value):
+    """Determine if the argument is an finite IEEE 754 value (i.e., is
+    not NaN, positive or negative inifinity)"""
+    return (_exponent(value)!=0x7ff)
+
+def isPosInf(value):
+    "Determine if the argument is a IEEE 754 positive infinity value"
+    return (_sign(value)==0 and _exponent(value)==0x7ff and \
+            _zero_mantissa(value))
+
+def isNegInf(value):
+    "Determine if the argument is a IEEE 754 negative infinity value"
+    return (_sign(value)==1 and _exponent(value)==0x7ff and \
+            _zero_mantissa(value))
+
+##
+## Functions to test public functions.
+## 
+
+def test_isNaN():
+    assert( not isNaN(PosInf) )
+    assert( not isNaN(NegInf) )
+    assert(     isNaN(NaN   ) )
+    assert( not isNaN(   1.0) )
+    assert( not isNaN(  -1.0) )
+
+def test_isInf():
+    assert(     isInf(PosInf) )
+    assert(     isInf(NegInf) )
+    assert( not isInf(NaN   ) )
+    assert( not isInf(   1.0) )
+    assert( not isInf(  -1.0) )
+
+def test_isFinite():
+    assert( not isFinite(PosInf) )
+    assert( not isFinite(NegInf) )
+    assert( not isFinite(NaN   ) )
+    assert(     isFinite(   1.0) )
+    assert(     isFinite(  -1.0) )
+
+def test_isPosInf():
+    assert(     isPosInf(PosInf) )
+    assert( not isPosInf(NegInf) )
+    assert( not isPosInf(NaN   ) )
+    assert( not isPosInf(   1.0) )
+    assert( not isPosInf(  -1.0) )
+
+def test_isNegInf():
+    assert( not isNegInf(PosInf) )
+    assert(     isNegInf(NegInf) )
+    assert( not isNegInf(NaN   ) )
+    assert( not isNegInf(   1.0) )
+    assert( not isNegInf(  -1.0) )
+
+# overall test
+def test():
+    test_isNaN()
+    test_isInf()
+    test_isFinite()
+    test_isPosInf()
+    test_isNegInf()
+
+if __name__ == "__main__":
+    test()
+