[Qemu-devel] [PATCH 1/6] softfloat: Add float16 type and float16 NaN handling functions

[Peter Maydell]

Add a float16 type to softfloat, rather than using bits16 directly.
Also add the missing functions float16_is_quiet_nan(),
float16_is_signaling_nan() and float16_maybe_silence_nan(),
which are needed for the float16 conversion routines.

Signed-off-by: Peter Maydell <address@hidden>
---
 fpu/softfloat-specialize.h |   59 ++++++++++++++++++++++++++++++++++++++++++++
 fpu/softfloat.c            |    8 +++---
 fpu/softfloat.h            |   12 +++++++-
 3 files changed, 73 insertions(+), 6 deletions(-)

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index eb644b2..bc9a66c 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -57,6 +57,65 @@ typedef struct {
 } commonNaNT;
 
 /*----------------------------------------------------------------------------
+| The pattern for a default generated half-precision NaN.
+*----------------------------------------------------------------------------*/
+#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
+
+/*----------------------------------------------------------------------------
+| Returns 1 if the half-precision floating-point value `a' is a quiet
+| NaN; otherwise returns 0.
+*----------------------------------------------------------------------------*/
+
+int float16_is_quiet_nan(float16 a)
+{
+#if SNAN_BIT_IS_ONE
+    return (((a >> 9) & 0x3F) == 0x3E) && (a & 0x1FF);
+#else
+    return ((a & ~0x8000) >= 0x7c80);
+#endif
+}
+
+/*----------------------------------------------------------------------------
+| Returns 1 if the half-precision floating-point value `a' is a signaling
+| NaN; otherwise returns 0.
+*----------------------------------------------------------------------------*/
+
+int float16_is_signaling_nan(float16 a)
+{
+#if SNAN_BIT_IS_ONE
+    return ((a & ~0x8000) >= 0x7c80);
+#else
+    return (((a >> 9) & 0x3F) == 0x3E) && (a & 0x1FF);
+#endif
+}
+
+/*----------------------------------------------------------------------------
+| Returns a quiet NaN if the half-precision floating point value `a' is a
+| signaling NaN; otherwise returns `a'.
+*----------------------------------------------------------------------------*/
+float16 float16_maybe_silence_nan(float16 a)
+{
+    if (float16_is_signaling_nan(a)) {
+#if SNAN_BIT_IS_ONE
+#  if defined(TARGET_MIPS) || defined(TARGET_SH4)
+        return float16_default_nan;
+#  else
+#    error Rules for silencing a signaling NaN are target-specific
+#  endif
+#else
+        a |= (1 << 9);
+#endif
+    }
+    return a;
+}
+
+/*----------------------------------------------------------------------------
 | The pattern for a default generated single-precision NaN.
 *----------------------------------------------------------------------------*/
 #if defined(TARGET_SPARC)
diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 17842f4..dc4492a 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -2713,15 +2713,15 @@ float32 float64_to_float32( float64 a STATUS_PARAM )
 | than the desired result exponent whenever `zSig' is a complete, normalized
 | significand.
 *----------------------------------------------------------------------------*/
-static bits16 packFloat16(flag zSign, int16 zExp, bits16 zSig)
+static float16 packFloat16(flag zSign, int16 zExp, bits16 zSig)
 {
     return (((bits32)zSign) << 15) + (((bits32)zExp) << 10) + zSig;
 }
 
 /* Half precision floats come in two formats: standard IEEE and "ARM" format.
    The latter gains extra exponent range by omitting the NaN/Inf encodings.  */
-  
-float32 float16_to_float32( bits16 a, flag ieee STATUS_PARAM )
+
+float32 float16_to_float32(float16 a, flag ieee STATUS_PARAM)
 {
     flag aSign;
     int16 aExp;
@@ -2753,7 +2753,7 @@ float32 float16_to_float32( bits16 a, flag ieee 
STATUS_PARAM )
     return packFloat32( aSign, aExp + 0x70, aSig << 13);
 }
 
-bits16 float32_to_float16( float32 a, flag ieee STATUS_PARAM)
+float16 float32_to_float16(float32 a, flag ieee STATUS_PARAM)
 {
     flag aSign;
     int16 aExp;
diff --git a/fpu/softfloat.h b/fpu/softfloat.h
index 4a5345c..f773d67 100644
--- a/fpu/softfloat.h
+++ b/fpu/softfloat.h
@@ -118,6 +118,7 @@ enum {
    sane ABI should be able to see though these structs.  However
    x86/gcc 3.x seems to struggle a bit, so leave them disabled by default.  */
 //#define USE_SOFTFLOAT_STRUCT_TYPES
+typedef uint16_t float16;
 #ifdef USE_SOFTFLOAT_STRUCT_TYPES
 typedef struct {
     uint32_t v;
@@ -253,8 +254,15 @@ float128 int64_to_float128( int64_t STATUS_PARAM );
 /*----------------------------------------------------------------------------
 | Software half-precision conversion routines.
 *----------------------------------------------------------------------------*/
-bits16 float32_to_float16( float32, flag STATUS_PARAM );
-float32 float16_to_float32( bits16, flag STATUS_PARAM );
+float16 float32_to_float16( float32, flag STATUS_PARAM );
+float32 float16_to_float32( float16, flag STATUS_PARAM );
+
+/*----------------------------------------------------------------------------
+| Software half-precision operations.
+*----------------------------------------------------------------------------*/
+int float16_is_quiet_nan( float16 );
+int float16_is_signaling_nan( float16 );
+float16 float16_maybe_silence_nan( float16 );
 
 /*----------------------------------------------------------------------------
 | Software IEC/IEEE single-precision conversion routines.
-- 
1.7.1