Implement a float16 directive for assembling 16 bit IEEE 754 floating point numbers for the AArch64 assembler.

The syntax of the directive is:

     .float16 <0-n decimal numbers>
e.g.
     .float16 0.5
     .float16 10.2, NaN, 452.09

The floats will always be encoded using the binary16 format as described in the
IEEE 754-2008 standard. There is no need to support Arm's alternative half-precision
format since AArch64 only supports the IEEE format.

gas	* config/tc-aarch64.c: Add float16 directive and add "Hh" to
	acceptable float characters.
	* doc/c-aarch64.texi: Documentation for float16 directive.
	* testsuite/gas/aarch64/float16-be.d: New test.
	* testsuite/gas/aarch64/float16-le.d: New test.
	* testsuite/gas/aarch64/float16.s: New test.
	* NEWS: Add NEWS entry.

gas/ChangeLog

@@ -1,3 +1,13 @@
+2019-08-22  Barnaby Wilks  <barnaby.wilks@arm.com>
+
+	* config/tc-aarch64.c: Add float16 directive and add "Hh" to
+	acceptable float characters.
+	* doc/c-aarch64.texi: Documentation for float16 directive.
+	* testsuite/gas/aarch64/float16-be.d: New test.
+	* testsuite/gas/aarch64/float16-le.d: New test.
+	* testsuite/gas/aarch64/float16.s: New test.
+	* NEWS: Add NEWS entry.
+
 2019-08-22  Kyrylo Tkachov <kyrylo.tkachov@arm.com>
 
 	* testsuite/gas/aarch64/sysreg-4.d: Update expected disassembly for

gas/NEWS

@@ -3,10 +3,10 @@
 * Add support for the Armv8.1-M Mainline and M-profile Vector Extension (MVE)
   instructions.
 
-* For MIPS, Add -m[no-]fix-loongson3-llsc option to fix (or not) Loongson3 LLSC
+* For MIPS, Add -m[no-]fix-loongson3-llsc option to fix (or not) Loongson3
-  Errata.  Add a --enable-mips-fix-loongson3-llsc=[yes|no] configure time option
+  LLSC Errata.  Add a --enable-mips-fix-loongson3-llsc=[yes|no] configure
-  to set the default behavior. Set the default if the configure option is not used
+  time option to set the default behavior. Set the default if the configure
-  to "no".
+  option is not used to "no".
 
 * Add support for the Arm Cortex-A76AE, Cortex-A77 and Cortex-M35P
   processors.
@@ -14,6 +14,11 @@
 * Add support for the AArch64 Cortex-A34, Cortex-A65, Cortex-A65AE,
   Cortex-A76AE, and Cortex-A77 processors.
 
+* Add .float16 directive for both Arm and AArch64 to allow encoding of 16-bit
+  floating point literals.  Add .float16_format directive and
+  -mfp16-format=[ieee|alternative] option for Arm to control the format of the
+  encoding.
+
 Changes in 2.32:
 
 * Add -mvexwig=[0|1] option to x86 assembler to control encoding of

gas/config/tc-aarch64.c

@@ -529,7 +529,7 @@ const char EXP_CHARS[] = "eE";
 /* As in 0f12.456  */
 /* or	 0d1.2345e12  */
 
-const char FLT_CHARS[] = "rRsSfFdDxXeEpP";
+const char FLT_CHARS[] = "rRsSfFdDxXeEpPhH";
 
 /* Prefix character that indicates the start of an immediate value.  */
 #define is_immediate_prefix(C) ((C) == '#')
@@ -2106,6 +2106,7 @@ const pseudo_typeS md_pseudo_table[] = {
   {"dword", s_aarch64_elf_cons, 8},
   {"variant_pcs", s_variant_pcs, 0},
 #endif
+  {"float16", float_cons, 'h'},
   {0, 0, 0}
 };
 

gas/doc/c-aarch64.texi

@@ -358,6 +358,14 @@ The @code{.even} directive aligns the output on the next even byte
 boundary.
 
 @c FFFFFFFFFFFFFFFFFFFFFFFFFF
+
+@cindex @code{.float16} directive, AArch64
+@item .float16 @var{value [,...,value_n]}
+Place the half precision floating point representation of one or more
+floating-point values into the current section.
+The format used to encode the floating point values is always the
+IEEE 754-2008 half precision floating point format.
+
 @c GGGGGGGGGGGGGGGGGGGGGGGGGG
 @c HHHHHHHHHHHHHHHHHHHHHHHHHH
 @c IIIIIIIIIIIIIIIIIIIIIIIIII

gas/testsuite/gas/aarch64/float16-be.d

@@ -0,0 +1,11 @@
+# name: Big endian float16 literals (IEEE 754 format)
+# source: float16.s
+# objdump: -s --section=.data
+# as: -mbig-endian
+
+.*: +file format .*
+
+Contents of section \.data:
+ 0000 4a002fdf 1c197bff 000103ff 04003c00.*
+ 0010 3c017fff 7c00fc00 00008000 bc00bbe7.*
+ 0020 fbff4200 4a00603e.*

gas/testsuite/gas/aarch64/float16-le.d

@@ -0,0 +1,11 @@
+# name: Little endian float16 literals (IEEE 754 format)
+# source: float16.s
+# objdump: -s --section=.data
+# as: -mlittle-endian
+
+.*: +file format .*
+
+Contents of section \.data:
+ 0000 004adf2f 191cff7b 0100ff03 0004003c.*
+ 0010 013cff7f 007c00fc 00000080 00bce7bb.*
+ 0020 fffb0042 004a3e60.*

gas/testsuite/gas/aarch64/float16.s

@@ -0,0 +1,19 @@
+.data
+	.float16 12.0
+	.float16 0.123
+	.float16 0.004
+	.float16 65504
+	.float16 5.9605e-8
+	.float16 6.0976e-5
+	.float16 6.1035e-5
+	.float16 1
+	.float16 1.001
+	.float16 NaN
+	.float16 +Inf
+	.float16 -Inf
+	.float16 +0
+	.float16 -0
+	.float16 -1
+	.float16 -0.98765
+	.float16 -65504
+	.float16 3.0, 12.0, 543.123