[PATCH] ldbl-128ibm: make ieee754.h work with IEEE 128 long double

[PATCH] ldbl-128ibm: make ieee754.h work with IEEE 128 long double

[Paul E. Murphy]

Instead of attempting something more creative, just copy
the small struct from ldbl-128 and enable it when IEEE
long double is present, and update the ibm long double
variant if supported.

Likewise, provide a shadow copy of math_ldbl.h to prevent
the ibm128 specific long double header from poisoning
unrelated files due to it's usage in math_private.h.
---
 .../ieee754/ldbl-128ibm-compat/math_ldbl.h    | 30 ++++++++
 sysdeps/ieee754/ldbl-128ibm/ieee754.h         | 68 ++++++++++++++++++-
 2 files changed, 96 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/ieee754/ldbl-128ibm-compat/math_ldbl.h

diff --git a/sysdeps/ieee754/ldbl-128ibm-compat/math_ldbl.h b/sysdeps/ieee754/ldbl-128ibm-compat/math_ldbl.h
new file mode 100644
index 0000000000..352617e178
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm-compat/math_ldbl.h
@@ -0,0 +1,30 @@
+/* Manipulation of the bit representation of 'long double' quantities.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_LDBL_H_IBM128_COMPAT
+#define _MATH_LDBL_H_IBM128_COMPAT 1
+
+#include <bits/floatn.h>
+
+/* Trampoline in the ldbl-128ibm headers if building against the
+   old abi.  Otherwise, we have nothing to add. */
+#if __LONG_DOUBLE_USES_FLOAT128 == 0
+#include_next <math_ldbl.h>
+#endif
+
+#endif /* _MATH_LDBL_H_IBM128_COMPAT */
diff --git a/sysdeps/ieee754/ldbl-128ibm/ieee754.h b/sysdeps/ieee754/ldbl-128ibm/ieee754.h
index 87c64fc316..ef251613f5 100644
--- a/sysdeps/ieee754/ldbl-128ibm/ieee754.h
+++ b/sysdeps/ieee754/ldbl-128ibm/ieee754.h
@@ -21,6 +21,7 @@
 #include <features.h>
 
 #include <bits/endian.h>
+#include <bits/floatn.h>
 
 __BEGIN_DECLS
 
@@ -111,6 +112,65 @@ union ieee754_double
 #define IEEE754_DOUBLE_BIAS	0x3ff /* Added to exponent.  */
 
 
+#if __LONG_DOUBLE_USES_FLOAT128 == 1
+/* long double is IEEE 128 bit */
+union ieee854_long_double
+  {
+    long double d;
+
+    /* This is the IEEE 854 quad-precision format.  */
+    struct
+      {
+#if	__BYTE_ORDER == __BIG_ENDIAN
+	unsigned int negative:1;
+	unsigned int exponent:15;
+	/* Together these comprise the mantissa.  */
+	unsigned int mantissa0:16;
+	unsigned int mantissa1:32;
+	unsigned int mantissa2:32;
+	unsigned int mantissa3:32;
+#endif				/* Big endian.  */
+#if	__BYTE_ORDER == __LITTLE_ENDIAN
+	/* Together these comprise the mantissa.  */
+	unsigned int mantissa3:32;
+	unsigned int mantissa2:32;
+	unsigned int mantissa1:32;
+	unsigned int mantissa0:16;
+	unsigned int exponent:15;
+	unsigned int negative:1;
+#endif				/* Little endian.  */
+      } ieee;
+
+    /* This format makes it easier to see if a NaN is a signalling NaN.  */
+    struct
+      {
+#if	__BYTE_ORDER == __BIG_ENDIAN
+	unsigned int negative:1;
+	unsigned int exponent:15;
+	unsigned int quiet_nan:1;
+	/* Together these comprise the mantissa.  */
+	unsigned int mantissa0:15;
+	unsigned int mantissa1:32;
+	unsigned int mantissa2:32;
+	unsigned int mantissa3:32;
+#else
+	/* Together these comprise the mantissa.  */
+	unsigned int mantissa3:32;
+	unsigned int mantissa2:32;
+	unsigned int mantissa1:32;
+	unsigned int mantissa0:15;
+	unsigned int quiet_nan:1;
+	unsigned int exponent:15;
+	unsigned int negative:1;
+#endif
+      } ieee_nan;
+  };
+
+#define IEEE854_LONG_DOUBLE_BIAS 0x3fff /* Added to exponent.  */
+#endif
+
+
+#if __LONG_DOUBLE_USES_FLOAT128 == 0 || __GNUC_PREREQ (7, 0)
 /* IBM extended format for long double.
 
    Each long double is made up of two IEEE doubles.  The value of the
@@ -121,12 +181,16 @@ union ieee754_double
    -0.0.  No other requirements are made; so, for example, 1.0 may be
    represented as (1.0, +0.0) or (1.0, -0.0), and the low part of a
    NaN is don't-care.  */
-
 union ibm_extended_long_double
   {
-    long double ld;
+#if __LONG_DOUBLE_USES_FLOAT128 == 1 && __GNUC_PREREQ (7, 0)
+   __ibm128 ld;
+# else
+   long double ld;
+# endif
     union ieee754_double d[2];
    };
+#endif
 
 __END_DECLS
 
-- 
2.21.1

Re: [PATCH] ldbl-128ibm: make ieee754.h work with IEEE 128 long double

[Tulio Magno Quites Machado Filho]

"Paul E. Murphy" <murphyp@linux.vnet.ibm.com> writes:

> Instead of attempting something more creative, just copy
> the small struct from ldbl-128 and enable it when IEEE
> long double is present, and update the ibm long double
> variant if supported.
>
> Likewise, provide a shadow copy of math_ldbl.h to prevent
> the ibm128 specific long double header from poisoning
> unrelated files due to it's usage in math_private.h.

LGTM with a cosmetic change.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

> @@ -121,12 +181,16 @@ union ieee754_double
>     -0.0.  No other requirements are made; so, for example, 1.0 may be
>     represented as (1.0, +0.0) or (1.0, -0.0), and the low part of a
>     NaN is don't-care.  */
> -
>  union ibm_extended_long_double
>    {
> -    long double ld;
> +#if __LONG_DOUBLE_USES_FLOAT128 == 1 && __GNUC_PREREQ (7, 0)

This is missing an indentation, like the else and endif clauses below.

-- 
Tulio Magno

Re: [PATCH] ldbl-128ibm: make ieee754.h work with IEEE 128 long double

[Paul E Murphy]

Pushed with cosmetic fix after verification against all 
build-many-glibcs.py targets.  Thank you for your review Tulio.

On 2/18/20 8:05 AM, Tulio Magno Quites Machado Filho wrote:
> "Paul E. Murphy" <murphyp@linux.vnet.ibm.com> writes:
> 
>> Instead of attempting something more creative, just copy
>> the small struct from ldbl-128 and enable it when IEEE
>> long double is present, and update the ibm long double
>> variant if supported.
>>
>> Likewise, provide a shadow copy of math_ldbl.h to prevent
>> the ibm128 specific long double header from poisoning
>> unrelated files due to it's usage in math_private.h.
> 
> LGTM with a cosmetic change.
> 
> Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
> 
>> @@ -121,12 +181,16 @@ union ieee754_double
>>      -0.0.  No other requirements are made; so, for example, 1.0 may be
>>      represented as (1.0, +0.0) or (1.0, -0.0), and the low part of a
>>      NaN is don't-care.  */
>> -
>>   union ibm_extended_long_double
>>     {
>> -    long double ld;
>> +#if __LONG_DOUBLE_USES_FLOAT128 == 1 && __GNUC_PREREQ (7, 0)
> 
> This is missing an indentation, like the else and endif clauses below.
>