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Diffstat (limited to 'POSIX.STD')
| -rw-r--r-- | POSIX.STD | 63 |
1 files changed, 63 insertions, 0 deletions
@@ -1,3 +1,66 @@ + Copyright (C) 1992, 1995, 1998, 2001, 2006, 2007 + Free Software Foundation, Inc. + + Copying and distribution of this file, with or without modification, + are permitted in any medium without royalty provided the copyright + notice and this notice are preserved. +-------------------------------------------------------------------------- +Mon May 7 14:38:32 IDT 2007 +============================ + +Thanks to Andrew Schorr for some of the wording here. + +<quote> +The Open Group awk specification says that a string value shall +be converted to a numeric value using the ISO C standard atof() +function. The awk spec is here: + + http://www.opengroup.org/onlinepubs/009695399/utilities/awk.html + +And the ISO C standard says that atof() shall work the same way +as strtod(), and strtod() must recognize the IEEE special values +for NaN (not-a-number) and Infinity. +</quote> + +As a result, more than one gawk user has come to the conclusion that +gawk is not standard compliant since it does not support converting +these special values. + +Similar reasoning has led other users to conclude that gawk must also +support input data in the format of C99-style hexadecimal floating point +numbers. + +I, Arnold Robbins, the gawk maintainer, feel that while these interpretations +of the standard can be made, they are _unintended_ side effects of the +change in the POSIX standard to refer to the ISO C99 standard everywhere. + +With resepct to hexadecimal floating point, historically, AWK has always +supported the input of only decimal numbers. Adding such a facility is +likely to break many programs, very badly, and is a very big departure +from historical practice. + +With respect to "NaN" and "Inf" values, many people point out that Unix +awk and mawk "support the standard" and print such values in their output. +This is _accidental_ support, since these programs are relying on the +system library version of strtod/atof to do the work. If compiled on a +system without such library support, those programs do NOT support the +special IEEE values. + +These special interpretations introduce a large departure from existing +practice: + + # Thanks to Brian Kernighan for this great example + $ nawk 'BEGIN { print "Nancy Reagan" + 0 }' + nan + +This is just plain wrong. String values with no leading digits must +continue to convert to numeric zero. + +The POSIX people have been asked to clarify these issues, and not recently, +but have not, to my knowledge, done so. Further discussion is provided +in the node "POSIX Floating Point Problems" in the gawk manual. + +---------- Stuff below this line is of historical interest only ---------- March 2001: It looks like the revised 1003.2 standard will actually follow the |