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Half precision floating point numbers will be encoded using the IEEE 754 half precision floating point format - 16 bits in total, 1 for sign, 5 for exponent and 10 bits of mantissa. This patch implements the float16 directive for both the IEEE 754 format and the Arm alternative format for the Arm backend. The syntax of the directive is: .float16 <0-n decimal numbers> e.g. .float16 12.0 .float16 0.23, 433.1, 0.06 The Arm alternative format is almost identical to the IEEE 754 format, except that it doesn't encode for NaNs or Infinity (instead an exponent of 0x1F represents a normalized number in the range 65536 to 131008). The alternative format is documented in the reference manual: https://static.docs.arm.com/ddi0487/db/DDI0487D_b_armv8_arm.pdf?_ga=2.72318806.49764181.1561632697-999473562.1560847439 Which format is used is controlled by the .float16_format <format> directive, where if <format> = ieee, then use the IEEE 754 half-precision format else if <format> = alternative, then use the Arm alternative format Or the format can be set on the command line via the -mfp16-format option that has a similar syntax. -mfp16-format=<ieee|alternative>. This also fixes the format and it cannot be changed by any directives. Once the format has been set (either by the command line option or a directive) it cannot be changed, and any attempts to change it (i.e. with the float16_format directive) will result in a warning and the line being ignored. For ELF targets the appropriate EABI attribute will be written out at the end of assembling if the format has been explicitly specified. If no format has been explicitly specified then no EABI attributes will be written. If the format is not explicitly specified then any float16 directives are encoding using the IEEE 754-2008 format by default until the format is fixed or changed with the float16_format directive. gas * config/tc-arm.c (enum fp_16bit_format): Add enum to represent the 2 float16 encodings. (md_atof): Set precision for float16 type. (arm_is_largest_exponent_ok): Check for whether to encode with the IEEE or alternative format. (set_fp16_format): Parse a float16_format directive. (arm_parse_fp16_opt): Parse the fp16-format command line option. (aeabi_set_public_attributes): For ELF encode the FP16 format EABI attribute. * config/tc-arm.h (TC_LARGEST_EXPONENT_IS_NORMAL): Macro that expands to arm_is_largest_exponent_ok. (arm_is_largest_exponent_ok): Add prototype for arm_is_largest_exponent_ok function. * doc/c-arm.texi: Add documentation for .float16, .float16_format and -mfp16-format= * testsuite/gas/arm/float16-bad.d: New test. * testsuite/gas/arm/float16-bad.l: New test. * testsuite/gas/arm/float16-bad.s: New test. * testsuite/gas/arm/float16-be.d: New test. * testsuite/gas/arm/float16-format-bad.d: New test. * testsuite/gas/arm/float16-format-bad.l: New test. * testsuite/gas/arm/float16-format-bad.s: New test. * testsuite/gas/arm/float16-format-opt-bad.d: New test. * testsuite/gas/arm/float16-format-opt-bad.l: New test. * testsuite/gas/arm/float16-le.d: New test. * testsuite/gas/arm/float16.s: New test. * testsuite/gas/arm/float16-eabi-alternative-format.d: New test. * testsuite/gas/arm/float16-eabi-ieee-format.d: New test. * testsuite/gas/arm/float16-eabi-no-format.d: New test. * testsuite/gas/arm/float16-eabi.s: New test. * config/atof-ieee.c (H_PRECISION): Macro for precision of float16 type. (atof_ieee): Set precision and exponent bits for encoding float16 types. (gen_to_words): NaN and Infinity encoding for float16. (ieee_md_atof): Set precision for encoding float16 type.
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.