softfloat: Add float16 type and float16 NaN handling functions

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 <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

3 files changed, 116 insertions, 10 deletions

diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index eb644b2..495f6f3 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -57,6 +57,69 @@ typedef struct {
 } commonNaNT;
 
 /*----------------------------------------------------------------------------
+| The pattern for a default generated half-precision NaN.
+*----------------------------------------------------------------------------*/
+#if defined(TARGET_ARM)
+#define float16_default_nan make_float16(0x7E00)
+#elif SNAN_BIT_IS_ONE
+#define float16_default_nan make_float16(0x7DFF)
+#else
+#define float16_default_nan make_float16(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_)
+{
+    uint16_t a = float16_val(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_)
+{
+    uint16_t a = float16_val(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
+        uint16_t a = float16_val(a_);
+        a |= (1 << 9);
+        return make_float16(a);
+#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..635c74c 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -67,6 +67,33 @@ void set_floatx80_rounding_precision(int val STATUS_PARAM)
 #endif
 
 /*----------------------------------------------------------------------------
+| Returns the fraction bits of the half-precision floating-point value `a'.
+*----------------------------------------------------------------------------*/
+
+INLINE uint32_t extractFloat16Frac(float16 a)
+{
+    return float16_val(a) & 0x3ff;
+}
+
+/*----------------------------------------------------------------------------
+| Returns the exponent bits of the half-precision floating-point value `a'.
+*----------------------------------------------------------------------------*/
+
+INLINE int16 extractFloat16Exp(float16 a)
+{
+    return (float16_val(a) >> 10) & 0x1f;
+}
+
+/*----------------------------------------------------------------------------
+| Returns the sign bit of the single-precision floating-point value `a'.
+*----------------------------------------------------------------------------*/
+
+INLINE flag extractFloat16Sign(float16 a)
+{
+    return float16_val(a)>>15;
+}
+
+/*----------------------------------------------------------------------------
 | Takes a 64-bit fixed-point value `absZ' with binary point between bits 6
 | and 7, and returns the properly rounded 32-bit integer corresponding to the
 | input.  If `zSign' is 1, the input is negated before being converted to an
@@ -2713,23 +2740,24 @@ 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;
+    return make_float16(
+        (((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;
     bits32 aSig;
 
-    aSign = a >> 15;
-    aExp = (a >> 10) & 0x1f;
-    aSig = a & 0x3ff;
+    aSign = extractFloat16Sign(a);
+    aExp = extractFloat16Exp(a);
+    aSig = extractFloat16Frac(a);
 
     if (aExp == 0x1f && ieee) {
         if (aSig) {
@@ -2753,7 +2781,7 @@ 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..2296adb 100644
--- a/fpu/softfloat.h
+++ b/fpu/softfloat.h
@@ -120,6 +120,11 @@ enum {
 //#define USE_SOFTFLOAT_STRUCT_TYPES
 #ifdef USE_SOFTFLOAT_STRUCT_TYPES
 typedef struct {
+    uint16_t v;
+} float16;
+#define float16_val(x) (((float16)(x)).v)
+#define make_float16(x) __extension__ ({ float16 f16_val = {x}; f16_val; })
+typedef struct {
     uint32_t v;
 } float32;
 /* The cast ensures an error if the wrong type is passed.  */
@@ -131,10 +136,13 @@ typedef struct {
 #define float64_val(x) (((float64)(x)).v)
 #define make_float64(x) __extension__ ({ float64 f64_val = {x}; f64_val; })
 #else
+typedef uint16_t float16;
 typedef uint32_t float32;
 typedef uint64_t float64;
+#define float16_val(x) (x)
 #define float32_val(x) (x)
 #define float64_val(x) (x)
+#define make_float16(x) (x)
 #define make_float32(x) (x)
 #define make_float64(x) (x)
 #endif
@@ -253,8 +261,15 @@ 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.