[Qemu-devel] [PATCH v2 3/4] softfloat: Revert and reimplement remaining parts of b645bb4885 and 5a6932d51d

[Peter Maydell <peter.maydell@linaro.org>]

Revert the parts of commits b645bb4885 and 5a6932d51d which are still
in the codebase and under a SoftFloat-2b license.

Reimplement support for architectures where the most significant bit
in the mantissa is 1 for a signaling NaN rather than a quiet NaN,
by adding handling for SNAN_BIT_IS_ONE being set to the functions
which test values for NaN-ness.

This includes restoring the bugfixes lost in the reversion where
some of the float*_is_quiet_nan() functions were returning true
for both signaling and quiet NaNs.

[This is a mechanical squashing together of two separate "revert"
and "reimplement" patches.]

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 fpu/softfloat-specialize.h | 57 +++++++++++++++++++++++-----------------------
 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index 39335b4..ef77e28 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -33,10 +33,14 @@ this code that are retained.
 ===============================================================================
 */
 
+/* Does the target distinguish signaling NaNs from non-signaling NaNs
+ * by setting the most significant bit of the mantissa for a signaling NaN?
+ * (The more common choice is to have it be zero for SNaN and one for QNaN.)
+ */
 #if defined(TARGET_MIPS) || defined(TARGET_SH4) || defined(TARGET_UNICORE32)
-#define SNAN_BIT_IS_ONE		1
+#define SNAN_BIT_IS_ONE 1
 #else
-#define SNAN_BIT_IS_ONE		0
+#define SNAN_BIT_IS_ONE 0
 #endif
 
 #if defined(TARGET_XTENSA)
@@ -79,7 +83,7 @@ const float64 float64_default_nan = const_float64(LIT64( 0x7FFFFFFFFFFFFFFF ));
 #elif defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_ALPHA)
 const float64 float64_default_nan = const_float64(LIT64( 0x7FF8000000000000 ));
 #elif SNAN_BIT_IS_ONE
-const float64 float64_default_nan = const_float64(LIT64( 0x7FF7FFFFFFFFFFFF ));
+const float64 float64_default_nan = const_float64(LIT64(0x7FF7FFFFFFFFFFFF));
 #else
 const float64 float64_default_nan = const_float64(LIT64( 0xFFF8000000000000 ));
 #endif
@@ -89,7 +93,7 @@ const float64 float64_default_nan = const_float64(LIT64( 0xFFF8000000000000 ));
 *----------------------------------------------------------------------------*/
 #if SNAN_BIT_IS_ONE
 #define floatx80_default_nan_high 0x7FFF
-#define floatx80_default_nan_low  LIT64( 0xBFFFFFFFFFFFFFFF )
+#define floatx80_default_nan_low  LIT64(0xBFFFFFFFFFFFFFFF)
 #else
 #define floatx80_default_nan_high 0xFFFF
 #define floatx80_default_nan_low  LIT64( 0xC000000000000000 )
@@ -103,8 +107,8 @@ const floatx80 floatx80_default_nan
 | `low' values hold the most- and least-significant bits, respectively.
 *----------------------------------------------------------------------------*/
 #if SNAN_BIT_IS_ONE
-#define float128_default_nan_high LIT64( 0x7FFF7FFFFFFFFFFF )
-#define float128_default_nan_low  LIT64( 0xFFFFFFFFFFFFFFFF )
+#define float128_default_nan_high LIT64(0x7FFF7FFFFFFFFFFF)
+#define float128_default_nan_low  LIT64(0xFFFFFFFFFFFFFFFF)
 #else
 #define float128_default_nan_high LIT64( 0xFFFF800000000000 )
 #define float128_default_nan_low  LIT64( 0x0000000000000000 )
@@ -255,9 +259,9 @@ int float32_is_quiet_nan( float32 a_ )
 {
     uint32_t a = float32_val(a_);
 #if SNAN_BIT_IS_ONE
-    return ( ( ( a>>22 ) & 0x1FF ) == 0x1FE ) && ( a & 0x003FFFFF );
+    return (((a >> 22) & 0x1ff) == 0x1fe) && (a & 0x003fffff);
 #else
-    return ( 0xFF800000 <= (uint32_t) ( a<<1 ) );
+    return ((uint32_t)(a << 1) >= 0xff800000);
 #endif
 }
 
@@ -270,7 +274,7 @@ int float32_is_signaling_nan( float32 a_ )
 {
     uint32_t a = float32_val(a_);
 #if SNAN_BIT_IS_ONE
-    return ( 0xFF800000 <= (uint32_t) ( a<<1 ) );
+    return ((uint32_t)(a << 1) >= 0xff800000);
 #else
     return ( ( ( a>>22 ) & 0x1FF ) == 0x1FE ) && ( a & 0x003FFFFF );
 #endif
@@ -663,11 +667,10 @@ int float64_is_quiet_nan( float64 a_ )
 {
     uint64_t a = float64_val(a_);
 #if SNAN_BIT_IS_ONE
-    return
-           ( ( ( a>>51 ) & 0xFFF ) == 0xFFE )
-        && ( a & LIT64( 0x0007FFFFFFFFFFFF ) );
+    return (((a >> 51) & 0xfff) == 0xffe)
+           && (a & 0x0007ffffffffffffULL);
 #else
-    return ( LIT64( 0xFFF0000000000000 ) <= (uint64_t) ( a<<1 ) );
+    return ((a << 1) >= 0xfff0000000000000ULL);
 #endif
 }
 
@@ -680,7 +683,7 @@ int float64_is_signaling_nan( float64 a_ )
 {
     uint64_t a = float64_val(a_);
 #if SNAN_BIT_IS_ONE
-    return ( LIT64( 0xFFF0000000000000 ) <= (uint64_t) ( a<<1 ) );
+    return ((a << 1) >= 0xfff0000000000000ULL);
 #else
     return
            ( ( ( a>>51 ) & 0xFFF ) == 0xFFE )
@@ -864,11 +867,10 @@ int floatx80_is_quiet_nan( floatx80 a )
 #if SNAN_BIT_IS_ONE
     uint64_t aLow;
 
-    aLow = a.low & ~ LIT64( 0x4000000000000000 );
-    return
-           ( ( a.high & 0x7FFF ) == 0x7FFF )
-        && (uint64_t) ( aLow<<1 )
-        && ( a.low == aLow );
+    aLow = a.low & ~0x4000000000000000ULL;
+    return ((a.high & 0x7fff) == 0x7fff)
+        && (aLow << 1)
+        && (a.low == aLow);
 #else
     return ( ( a.high & 0x7FFF ) == 0x7FFF )
         && (LIT64( 0x8000000000000000 ) <= ((uint64_t) ( a.low<<1 )));
@@ -884,8 +886,8 @@ int floatx80_is_quiet_nan( floatx80 a )
 int floatx80_is_signaling_nan( floatx80 a )
 {
 #if SNAN_BIT_IS_ONE
-    return ( ( a.high & 0x7FFF ) == 0x7FFF )
-        && (LIT64( 0x8000000000000000 ) <= ((uint64_t) ( a.low<<1 )));
+    return ((a.high & 0x7fff) == 0x7fff)
+        && ((a.low << 1) >= 0x8000000000000000ULL);
 #else
     uint64_t aLow;
 
@@ -1029,13 +1031,12 @@ int float128_is_signaling_nan(float128 a_)
 int float128_is_quiet_nan( float128 a )
 {
 #if SNAN_BIT_IS_ONE
-    return
-           ( ( ( a.high>>47 ) & 0xFFFF ) == 0xFFFE )
-        && ( a.low || ( a.high & LIT64( 0x00007FFFFFFFFFFF ) ) );
+    return (((a.high >> 47) & 0xffff) == 0xfffe)
+        && (a.low || (a.high & 0x00007fffffffffffULL));
 #else
     return
-           ( LIT64( 0xFFFE000000000000 ) <= (uint64_t) ( a.high<<1 ) )
-        && ( a.low || ( a.high & LIT64( 0x0000FFFFFFFFFFFF ) ) );
+        ((a.high << 1) >= 0xffff000000000000)
+        && (a.low || (a.high & 0x0000ffffffffffffULL));
 #endif
 }
 
@@ -1048,8 +1049,8 @@ int float128_is_signaling_nan( float128 a )
 {
 #if SNAN_BIT_IS_ONE
     return
-           ( LIT64( 0xFFFE000000000000 ) <= (uint64_t) ( a.high<<1 ) )
-        && ( a.low || ( a.high & LIT64( 0x0000FFFFFFFFFFFF ) ) );
+        ((a.high << 1) >= 0xffff000000000000)
+        && (a.low || (a.high & 0x0000ffffffffffffULL));
 #else
     return
            ( ( ( a.high>>47 ) & 0xFFFF ) == 0xFFFE )
-- 
1.9.1