[Qemu-devel] [PATCH 5/6] softfloat: reimplement SNAN_BIT_IS_ONE support

[Peter Maydell]

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.

Signed-off-by: Peter Maydell <address@hidden>
---
 fpu/softfloat-specialize.h | 74 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 70 insertions(+), 4 deletions(-)

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index 187cdf6..6de66ce 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -33,6 +33,16 @@ 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
+#else
+#define SNAN_BIT_IS_ONE 0
+#endif
+
 #if defined(TARGET_XTENSA)
 /* Define for architectures which deviate from IEEE in not supporting
  * signaling NaNs (so all NaNs are treated as quiet).
@@ -59,6 +69,8 @@ const float32 float32_default_nan = const_float32(0x7FFFFFFF);
 #elif defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_ALPHA) || \
       defined(TARGET_XTENSA)
 const float32 float32_default_nan = const_float32(0x7FC00000);
+#elif SNAN_BIT_IS_ONE
+const float32 float32_default_nan = const_float32(0xFF800000);
 #else
 const float32 float32_default_nan = const_float32(0xFFC00000);
 #endif
@@ -70,6 +82,8 @@ const float32 float32_default_nan = const_float32(0xFFC00000);
 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(0xFFF0000000000000));
 #else
 const float64 float64_default_nan = const_float64(LIT64( 0xFFF8000000000000 ));
 #endif
@@ -77,8 +91,13 @@ const float64 float64_default_nan = const_float64(LIT64( 
0xFFF8000000000000 ));
 /*----------------------------------------------------------------------------
 | The pattern for a default generated extended double-precision NaN.
 *----------------------------------------------------------------------------*/
+#if SNAN_BIT_IS_ONE
+#define floatx80_default_nan_high 0xFFFF
+#define floatx80_default_nan_low  LIT64(0x8000000000000000)
+#else
 #define floatx80_default_nan_high 0xFFFF
 #define floatx80_default_nan_low  LIT64( 0xC000000000000000 )
+#endif
 
 const floatx80 floatx80_default_nan
     = make_floatx80_init(floatx80_default_nan_high, floatx80_default_nan_low);
@@ -87,8 +106,13 @@ const floatx80 floatx80_default_nan
 | The pattern for a default generated quadruple-precision NaN.  The `high' and
 | `low' values hold the most- and least-significant bits, respectively.
 *----------------------------------------------------------------------------*/
+#if SNAN_BIT_IS_ONE
+#define float128_default_nan_high LIT64(0xFFFF000000000000)
+#define float128_default_nan_low  LIT64(0x0000000000000000)
+#else
 #define float128_default_nan_high LIT64( 0xFFFF800000000000 )
 #define float128_default_nan_low  LIT64( 0x0000000000000000 )
+#endif
 
 const float128 float128_default_nan
     = make_float128_init(float128_default_nan_high, float128_default_nan_low);
@@ -234,7 +258,11 @@ int float32_is_signaling_nan(float32 a_)
 int float32_is_quiet_nan( float32 a_ )
 {
     uint32_t a = float32_val(a_);
-    return ( 0xFF000000 <= (uint32_t) ( a<<1 ) );
+#if SNAN_BIT_IS_ONE
+    return (((a >> 22) & 0x1ff) == 0x1fe) && (a & 0x003fffff);
+#else
+    return ((uint32_t)(a << 1) >= 0xff800000);
+#endif
 }
 
 /*----------------------------------------------------------------------------
@@ -245,7 +273,11 @@ int float32_is_quiet_nan( float32 a_ )
 int float32_is_signaling_nan( float32 a_ )
 {
     uint32_t a = float32_val(a_);
+#if SNAN_BIT_IS_ONE
+    return ((uint32_t)(a << 1) >= 0xff800000);
+#else
     return ( ( ( a>>22 ) & 0x1FF ) == 0x1FE ) && ( a & 0x003FFFFF );
+#endif
 }
 #endif
 
@@ -634,7 +666,12 @@ int float64_is_signaling_nan(float64 a_)
 int float64_is_quiet_nan( float64 a_ )
 {
     uint64_t a = float64_val(a_);
-    return ( LIT64( 0xFFE0000000000000 ) <= (uint64_t) ( a<<1 ) );
+#if SNAN_BIT_IS_ONE
+    return (((a >> 51) & 0xfff) == 0xffe)
+           && (a & 0x0007ffffffffffffULL);
+#else
+    return ((a << 1) >= 0xfff0000000000000ULL);
+#endif
 }
 
 /*----------------------------------------------------------------------------
@@ -645,9 +682,13 @@ int float64_is_quiet_nan( float64 a_ )
 int float64_is_signaling_nan( float64 a_ )
 {
     uint64_t a = float64_val(a_);
+#if SNAN_BIT_IS_ONE
+    return ((a << 1) >= 0xfff0000000000000ULL);
+#else
     return
            ( ( ( a>>51 ) & 0xFFF ) == 0xFFE )
         && ( a & LIT64( 0x0007FFFFFFFFFFFF ) );
+#endif
 }
 #endif
 
@@ -823,8 +864,17 @@ int floatx80_is_signaling_nan(floatx80 a_)
 
 int floatx80_is_quiet_nan( floatx80 a )
 {
+#if SNAN_BIT_IS_ONE
+    uint64_t 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 )));
+#endif
 }
 
 /*----------------------------------------------------------------------------
@@ -835,6 +885,10 @@ int floatx80_is_quiet_nan( floatx80 a )
 
 int floatx80_is_signaling_nan( floatx80 a )
 {
+#if SNAN_BIT_IS_ONE
+    return ((a.high & 0x7fff) == 0x7fff)
+        && ((a.low << 1) >= 0x8000000000000000ULL);
+#else
     uint64_t aLow;
 
     aLow = a.low & ~ LIT64( 0x4000000000000000 );
@@ -842,6 +896,7 @@ int floatx80_is_signaling_nan( floatx80 a )
            ( ( a.high & 0x7FFF ) == 0x7FFF )
         && (uint64_t) ( aLow<<1 )
         && ( a.low == aLow );
+#endif
 }
 #endif
 
@@ -975,9 +1030,14 @@ 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 & 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
 }
 
 /*----------------------------------------------------------------------------
@@ -987,9 +1047,15 @@ int float128_is_quiet_nan( float128 a )
 
 int float128_is_signaling_nan( float128 a )
 {
+#if SNAN_BIT_IS_ONE
+    return
+        ((a.high << 1) >= 0xffff000000000000)
+        && (a.low || (a.high & 0x0000ffffffffffffULL));
+#else
     return
            ( ( ( a.high>>47 ) & 0xFFFF ) == 0xFFFE )
         && ( a.low || ( a.high & LIT64( 0x00007FFFFFFFFFFF ) ) );
+#endif
 }
 #endif
 
-- 
1.9.1