@node ax_c_float_words_bigendian
@unnumberedsec ax_c_float_words_bigendian

@majorheading Synopsis

@smallexample
AX_C_FLOAT_WORDS_BIGENDIAN([ACTION-IF-TRUE], [ACTION-IF-FALSE], [ACTION-IF-UNKNOWN])
@end smallexample

@majorheading Description

Checks the ordering of words within a multi-word float. This check is
necessary because on some systems (e.g. certain ARM systems), the float
word ordering can be different from the byte ordering. In a multi-word
float context, "big-endian" implies that the word containing the sign
bit is found in the memory location with the lowest address. This
implementation was inspired by the AC_C_BIGENDIAN macro in autoconf.

The endianness is detected by first compiling C code that contains a
special double float value, then grepping the resulting object file for
certain strings of ASCII values. The double is specially crafted to have
a binary representation that corresponds with a simple string. In this
implementation, the string "noonsees" was selected because the
individual word values ("noon" and "sees") are palindromes, thus making
this test byte-order agnostic. If grep finds the string "noonsees" in
the object file, the target platform stores float words in big-endian
order. If grep finds "seesnoon", float words are in little-endian order.
If neither value is found, the user is instructed to specify the
ordering.

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_c_float_words_bigendian.m4,latest
version of @file{ax_c_float_words_bigendian.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_c_float_words_bigendian.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2008 Daniel Amelang @email{dan@@amelang.net}}

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. This file is offered as-is, without any
warranty.