Softfloat: Add support to softfloat to return floatxx_default_nan when, the corresponding target status flag is set.

PATCH Superseded Christophe Lyon 2 participants 2 messages Feb 7, 2011

Share & tools

Christophe Lyon

author

2011-02-07 15:30 UTC #0 lore raw

PATCH v2 1/1 Softfloat: Add support to softfloat to return floatxx_default_nan when, the corresponding target status flag is set.

Some CPUs have a status flag imposing to return floatxx_default_nan whatever the input value, when converting from one FP format to another. Implement this, using the already existing default_nan_mode status flag (currently used on ARM and SH4 at the moment).

Signed-off-by Christophe Lyon <[email protected]>

---
Note that I am unsure whether it's useful to have a default (ie non-ARM) value for float16_default_nan and if the value I've used is right.

 fpu/softfloat-specialize.h |   57 ++++++++++++++++++++++++++++++++++++++++---
 fpu/softfloat.c            |   30 ++++++++++-------------
 2 files changed, 66 insertions(+), 21 deletions(-)

fpu/softfloat-specialize.h +53 -4

index 11521ce..997da36 100644
@@ -144,9 +144,14 @@ static commonNaNT float32ToCommonNaN( float32 a STATUS_PARAM )
 | precision floating-point format.
 *----------------------------------------------------------------------------*/
 
-static float32 commonNaNToFloat32( commonNaNT a )
+static float32 commonNaNToFloat32( commonNaNT a STATUS_PARAM)
 {
     bits32 mantissa = a.high>>41;
+
+    if ( STATUS(default_nan_mode) ) {
+        return float32_default_nan;
+    }
+
     if ( mantissa )
         return make_float32(
             ( ( (bits32) a.sign )<<31 ) | 0x7F800000 | ( a.high>>41 ) );

@@ -398,10 +403,14 @@ static commonNaNT float64ToCommonNaN( float64 a STATUS_PARAM)
 | precision floating-point format.
 *----------------------------------------------------------------------------*/
 
-static float64 commonNaNToFloat64( commonNaNT a )
+static float64 commonNaNToFloat64( commonNaNT a STATUS_PARAM)
 {
     bits64 mantissa = a.high>>12;
 
+    if ( STATUS(default_nan_mode) ) {
+        return float64_default_nan;
+    }
+
     if ( mantissa )
         return make_float64(
               ( ( (bits64) a.sign )<<63 )

@@ -451,6 +460,34 @@ static float64 propagateFloat64NaN( float64 a, float64 b STATUS_PARAM)
     }
 }
 
+/*----------------------------------------------------------------------------
+| The pattern for a default generated haft-precision NaN.
+*----------------------------------------------------------------------------*/
+#if defined(TARGET_ARM)
+#define float16_default_nan 0x7E00
+#else
+#define float16_default_nan 0xFE00
+#endif
+
+/*----------------------------------------------------------------------------
+| Returns the result of converting the canonical NaN `a' to the half-
+| precision floating-point format.
+*----------------------------------------------------------------------------*/
+
+static bits16 commonNaNToFloat16( commonNaNT a STATUS_PARAM)
+{
+    bits16 mantissa = a.high>>57;
+
+    if ( STATUS(default_nan_mode) ) {
+        return float16_default_nan;
+    }
+
+    if ( mantissa )
+        return (bits16)a.sign << 15 | 0x1F << 10 | mantissa;
+    else
+        return float16_default_nan;
+}
+
 #ifdef FLOATX80
 
 /*----------------------------------------------------------------------------

@@ -551,10 +588,16 @@ static commonNaNT floatx80ToCommonNaN( floatx80 a STATUS_PARAM)
 | double-precision floating-point format.
 *----------------------------------------------------------------------------*/
 
-static floatx80 commonNaNToFloatx80( commonNaNT a )
+static floatx80 commonNaNToFloatx80( commonNaNT a STATUS_PARAM)
 {
     floatx80 z;
 
+    if ( STATUS(default_nan_mode) ) {
+        z.low = floatx80_default_nan_low;
+        z.high = floatx80_default_nan_high;
+        return z;
+    }
+
     if (a.high)
         z.low = a.high;
     else

@@ -699,10 +742,16 @@ static commonNaNT float128ToCommonNaN( float128 a STATUS_PARAM)
 | precision floating-point format.
 *----------------------------------------------------------------------------*/
 
-static float128 commonNaNToFloat128( commonNaNT a )
+static float128 commonNaNToFloat128( commonNaNT a STATUS_PARAM)
 {
     float128 z;
 
+    if ( STATUS(default_nan_mode) ) {
+        z.low = float128_default_nan_low;
+        z.high = float128_default_nan_high;
+        return z;
+    }
+
     shift128Right( a.high, a.low, 16, &z.high, &z.low );
     z.high |= ( ( (bits64) a.sign )<<63 ) | LIT64( 0x7FFF000000000000 );
     return z;

fpu/softfloat.c +13 ~~-17~~

index 17842f4..abf14f1 100644
@@ -1534,7 +1534,7 @@ float64 float32_to_float64( float32 a STATUS_PARAM )
     aExp = extractFloat32Exp( a );
     aSign = extractFloat32Sign( a );
     if ( aExp == 0xFF ) {
-        if ( aSig ) return commonNaNToFloat64( float32ToCommonNaN( a STATUS_VAR ));
+        if ( aSig ) return commonNaNToFloat64( float32ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloat64( aSign, 0x7FF, 0 );
     }
     if ( aExp == 0 ) {

@@ -1566,7 +1566,7 @@ floatx80 float32_to_floatx80( float32 a STATUS_PARAM )
     aExp = extractFloat32Exp( a );
     aSign = extractFloat32Sign( a );
     if ( aExp == 0xFF ) {
-        if ( aSig ) return commonNaNToFloatx80( float32ToCommonNaN( a STATUS_VAR ) );
+        if ( aSig ) return commonNaNToFloatx80( float32ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloatx80( aSign, 0x7FFF, LIT64( 0x8000000000000000 ) );
     }
     if ( aExp == 0 ) {

@@ -1600,7 +1600,7 @@ float128 float32_to_float128( float32 a STATUS_PARAM )
     aExp = extractFloat32Exp( a );
     aSign = extractFloat32Sign( a );
     if ( aExp == 0xFF ) {
-        if ( aSig ) return commonNaNToFloat128( float32ToCommonNaN( a STATUS_VAR ) );
+        if ( aSig ) return commonNaNToFloat128( float32ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloat128( aSign, 0x7FFF, 0, 0 );
     }
     if ( aExp == 0 ) {

@@ -2689,7 +2689,7 @@ float32 float64_to_float32( float64 a STATUS_PARAM )
     aExp = extractFloat64Exp( a );
     aSign = extractFloat64Sign( a );
     if ( aExp == 0x7FF ) {
-        if ( aSig ) return commonNaNToFloat32( float64ToCommonNaN( a STATUS_VAR ) );
+        if ( aSig ) return commonNaNToFloat32( float64ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloat32( aSign, 0xFF, 0 );
     }
     shift64RightJamming( aSig, 22, &aSig );

@@ -2767,11 +2767,7 @@ bits16 float32_to_float16( float32 a, flag ieee STATUS_PARAM)
     aExp = extractFloat32Exp( a );
     aSign = extractFloat32Sign( a );
     if ( aExp == 0xFF ) {
-        if (aSig) {
-            /* Make sure correct exceptions are raised.  */
-            float32ToCommonNaN(a STATUS_VAR);
-            aSig |= 0x00400000;
-        }
+        if ( aSig ) return commonNaNToFloat16( float32ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloat16(aSign, 0x1f, aSig >> 13);
     }
     if (aExp == 0 && aSign == 0) {

@@ -2861,7 +2857,7 @@ floatx80 float64_to_floatx80( float64 a STATUS_PARAM )
     aExp = extractFloat64Exp( a );
     aSign = extractFloat64Sign( a );
     if ( aExp == 0x7FF ) {
-        if ( aSig ) return commonNaNToFloatx80( float64ToCommonNaN( a STATUS_VAR ) );
+        if ( aSig ) return commonNaNToFloatx80( float64ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloatx80( aSign, 0x7FFF, LIT64( 0x8000000000000000 ) );
     }
     if ( aExp == 0 ) {

@@ -2896,7 +2892,7 @@ float128 float64_to_float128( float64 a STATUS_PARAM )
     aExp = extractFloat64Exp( a );
     aSign = extractFloat64Sign( a );
     if ( aExp == 0x7FF ) {
-        if ( aSig ) return commonNaNToFloat128( float64ToCommonNaN( a STATUS_VAR ) );
+        if ( aSig ) return commonNaNToFloat128( float64ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         return packFloat128( aSign, 0x7FFF, 0, 0 );
     }
     if ( aExp == 0 ) {

@@ -3843,7 +3839,7 @@ float32 floatx80_to_float32( floatx80 a STATUS_PARAM )
     aSign = extractFloatx80Sign( a );
     if ( aExp == 0x7FFF ) {
         if ( (bits64) ( aSig<<1 ) ) {
-            return commonNaNToFloat32( floatx80ToCommonNaN( a STATUS_VAR ) );
+            return commonNaNToFloat32( floatx80ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         }
         return packFloat32( aSign, 0xFF, 0 );
     }

@@ -3871,7 +3867,7 @@ float64 floatx80_to_float64( floatx80 a STATUS_PARAM )
     aSign = extractFloatx80Sign( a );
     if ( aExp == 0x7FFF ) {
         if ( (bits64) ( aSig<<1 ) ) {
-            return commonNaNToFloat64( floatx80ToCommonNaN( a STATUS_VAR ) );
+            return commonNaNToFloat64( floatx80ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         }
         return packFloat64( aSign, 0x7FF, 0 );
     }

@@ -3900,7 +3896,7 @@ float128 floatx80_to_float128( floatx80 a STATUS_PARAM )
     aExp = extractFloatx80Exp( a );
     aSign = extractFloatx80Sign( a );
     if ( ( aExp == 0x7FFF ) && (bits64) ( aSig<<1 ) ) {
-        return commonNaNToFloat128( floatx80ToCommonNaN( a STATUS_VAR ) );
+        return commonNaNToFloat128( floatx80ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
     }
     shift128Right( aSig<<1, 0, 16, &zSig0, &zSig1 );
     return packFloat128( aSign, aExp, zSig0, zSig1 );

@@ -4863,7 +4859,7 @@ float32 float128_to_float32( float128 a STATUS_PARAM )
     aSign = extractFloat128Sign( a );
     if ( aExp == 0x7FFF ) {
         if ( aSig0 | aSig1 ) {
-            return commonNaNToFloat32( float128ToCommonNaN( a STATUS_VAR ) );
+            return commonNaNToFloat32( float128ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         }
         return packFloat32( aSign, 0xFF, 0 );
     }

@@ -4897,7 +4893,7 @@ float64 float128_to_float64( float128 a STATUS_PARAM )
     aSign = extractFloat128Sign( a );
     if ( aExp == 0x7FFF ) {
         if ( aSig0 | aSig1 ) {
-            return commonNaNToFloat64( float128ToCommonNaN( a STATUS_VAR ) );
+            return commonNaNToFloat64( float128ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         }
         return packFloat64( aSign, 0x7FF, 0 );
     }

@@ -4932,7 +4928,7 @@ floatx80 float128_to_floatx80( float128 a STATUS_PARAM )
     aSign = extractFloat128Sign( a );
     if ( aExp == 0x7FFF ) {
         if ( aSig0 | aSig1 ) {
-            return commonNaNToFloatx80( float128ToCommonNaN( a STATUS_VAR ) );
+            return commonNaNToFloatx80( float128ToCommonNaN( a STATUS_VAR ) STATUS_VAR );
         }
         return packFloatx80( aSign, 0x7FFF, LIT64( 0x8000000000000000 ) );
     }

Signature · 1 line

1.7.2.3

Peter Maydell

2011-02-07 16:48 UTC #1 lore raw

Quoted 1 line · Christophe Lyon

Note that I am unsure whether it's useful to have a default (ie non-ARM) value for float16_default_nan and if the value I've used is right.

We should set the default consistent with how we do it for the other types: special cases for various architectures, default for SNAN_BIT_IS_ONE is sign=0,exp=1....1, mantissa=01.....1; default for !SNAN_BIT_IS_ONE is sign=1,exp=1.....1,mantissa=0....0. So:

#if defined(TARGET_ARM)
#define float16_default_nan 0x7E00
#elif SNAN_BIT_IS_ONE
#define float16_default_nan 0x7DFF
#else
#define float16_default_nan 0xFE00
#endif

fpu/softfloat-specialize.h static float64 propagateFloat64NaN( float64 a, float64 b STATUS_PARAM) · line 489

Quoted 13 lines

fpu/softfloat-specialize.h +13 -0

+static bits16 commonNaNToFloat16( commonNaNT a STATUS_PARAM)
+{
+    bits16 mantissa = a.high>>57;
+
+    if ( STATUS(default_nan_mode) ) {
+        return float16_default_nan;
+    }
+
+    if ( mantissa )
+        return (bits16)a.sign << 15 | 0x1F << 10 | mantissa;
+    else
+        return float16_default_nan;
+}

Could we have some brackets around the shifts and some braces for this if(), please? (I know most of softfloat doesn't adhere to the qemu brace-standard, and I'm not going to ask for all those other ifs to change, but since this is a new function we might as well put in the braces for this one.)

thanks
-- PMM