softfloat: Implement fused multiply-add
Implement fused multiply-add as a softfloat primitive. This implements
"a+b*c" as a single step without any intermediate rounding; it is
specified in IEEE 754-2008 and implemented in a number of CPUs.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/fpu/softfloat-specialize.h b/fpu/softfloat-specialize.h
index c165205..c5e2dab 100644
--- a/fpu/softfloat-specialize.h
+++ b/fpu/softfloat-specialize.h
@@ -420,6 +420,82 @@
#endif
/*----------------------------------------------------------------------------
+| Select which NaN to propagate for a three-input operation.
+| For the moment we assume that no CPU needs the 'larger significand'
+| information.
+| Return values : 0 : a; 1 : b; 2 : c; 3 : default-NaN
+*----------------------------------------------------------------------------*/
+#if defined(TARGET_ARM)
+static int pickNaNMulAdd(flag aIsQNaN, flag aIsSNaN, flag bIsQNaN, flag bIsSNaN,
+ flag cIsQNaN, flag cIsSNaN, flag infzero STATUS_PARAM)
+{
+ /* For ARM, the (inf,zero,qnan) case sets InvalidOp and returns
+ * the default NaN
+ */
+ if (infzero && cIsQNaN) {
+ float_raise(float_flag_invalid STATUS_VAR);
+ return 3;
+ }
+
+ /* This looks different from the ARM ARM pseudocode, because the ARM ARM
+ * puts the operands to a fused mac operation (a*b)+c in the order c,a,b.
+ */
+ if (cIsSNaN) {
+ return 2;
+ } else if (aIsSNaN) {
+ return 0;
+ } else if (bIsSNaN) {
+ return 1;
+ } else if (cIsQNaN) {
+ return 2;
+ } else if (aIsQNaN) {
+ return 0;
+ } else {
+ return 1;
+ }
+}
+#elif defined(TARGET_PPC)
+static int pickNaNMulAdd(flag aIsQNaN, flag aIsSNaN, flag bIsQNaN, flag bIsSNaN,
+ flag cIsQNaN, flag cIsSNaN, flag infzero STATUS_PARAM)
+{
+ /* For PPC, the (inf,zero,qnan) case sets InvalidOp, but we prefer
+ * to return an input NaN if we have one (ie c) rather than generating
+ * a default NaN
+ */
+ if (infzero) {
+ float_raise(float_flag_invalid STATUS_VAR);
+ return 2;
+ }
+
+ /* If fRA is a NaN return it; otherwise if fRB is a NaN return it;
+ * otherwise return fRC. Note that muladd on PPC is (fRA * fRC) + frB
+ */
+ if (aIsSNaN || aIsQNaN) {
+ return 0;
+ } else if (cIsSNaN || cIsQNaN) {
+ return 2;
+ } else {
+ return 1;
+ }
+}
+#else
+/* A default implementation: prefer a to b to c.
+ * This is unlikely to actually match any real implementation.
+ */
+static int pickNaNMulAdd(flag aIsQNaN, flag aIsSNaN, flag bIsQNaN, flag bIsSNaN,
+ flag cIsQNaN, flag cIsSNaN, flag infzero STATUS_PARAM)
+{
+ if (aIsSNaN || aIsQNaN) {
+ return 0;
+ } else if (bIsSNaN || bIsQNaN) {
+ return 1;
+ } else {
+ return 2;
+ }
+}
+#endif
+
+/*----------------------------------------------------------------------------
| Takes two single-precision floating-point values `a' and `b', one of which
| is a NaN, and returns the appropriate NaN result. If either `a' or `b' is a
| signaling NaN, the invalid exception is raised.
@@ -460,6 +536,57 @@
}
/*----------------------------------------------------------------------------
+| Takes three single-precision floating-point values `a', `b' and `c', one of
+| which is a NaN, and returns the appropriate NaN result. If any of `a',
+| `b' or `c' is a signaling NaN, the invalid exception is raised.
+| The input infzero indicates whether a*b was 0*inf or inf*0 (in which case
+| obviously c is a NaN, and whether to propagate c or some other NaN is
+| implementation defined).
+*----------------------------------------------------------------------------*/
+
+static float32 propagateFloat32MulAddNaN(float32 a, float32 b,
+ float32 c, flag infzero STATUS_PARAM)
+{
+ flag aIsQuietNaN, aIsSignalingNaN, bIsQuietNaN, bIsSignalingNaN,
+ cIsQuietNaN, cIsSignalingNaN;
+ int which;
+
+ aIsQuietNaN = float32_is_quiet_nan(a);
+ aIsSignalingNaN = float32_is_signaling_nan(a);
+ bIsQuietNaN = float32_is_quiet_nan(b);
+ bIsSignalingNaN = float32_is_signaling_nan(b);
+ cIsQuietNaN = float32_is_quiet_nan(c);
+ cIsSignalingNaN = float32_is_signaling_nan(c);
+
+ if (aIsSignalingNaN | bIsSignalingNaN | cIsSignalingNaN) {
+ float_raise(float_flag_invalid STATUS_VAR);
+ }
+
+ which = pickNaNMulAdd(aIsQuietNaN, aIsSignalingNaN,
+ bIsQuietNaN, bIsSignalingNaN,
+ cIsQuietNaN, cIsSignalingNaN, infzero STATUS_VAR);
+
+ if (STATUS(default_nan_mode)) {
+ /* Note that this check is after pickNaNMulAdd so that function
+ * has an opportunity to set the Invalid flag.
+ */
+ return float32_default_nan;
+ }
+
+ switch (which) {
+ case 0:
+ return float32_maybe_silence_nan(a);
+ case 1:
+ return float32_maybe_silence_nan(b);
+ case 2:
+ return float32_maybe_silence_nan(c);
+ case 3:
+ default:
+ return float32_default_nan;
+ }
+}
+
+/*----------------------------------------------------------------------------
| Returns 1 if the double-precision floating-point value `a' is a quiet
| NaN; otherwise returns 0.
*----------------------------------------------------------------------------*/
@@ -596,6 +723,57 @@
}
/*----------------------------------------------------------------------------
+| Takes three double-precision floating-point values `a', `b' and `c', one of
+| which is a NaN, and returns the appropriate NaN result. If any of `a',
+| `b' or `c' is a signaling NaN, the invalid exception is raised.
+| The input infzero indicates whether a*b was 0*inf or inf*0 (in which case
+| obviously c is a NaN, and whether to propagate c or some other NaN is
+| implementation defined).
+*----------------------------------------------------------------------------*/
+
+static float64 propagateFloat64MulAddNaN(float64 a, float64 b,
+ float64 c, flag infzero STATUS_PARAM)
+{
+ flag aIsQuietNaN, aIsSignalingNaN, bIsQuietNaN, bIsSignalingNaN,
+ cIsQuietNaN, cIsSignalingNaN;
+ int which;
+
+ aIsQuietNaN = float64_is_quiet_nan(a);
+ aIsSignalingNaN = float64_is_signaling_nan(a);
+ bIsQuietNaN = float64_is_quiet_nan(b);
+ bIsSignalingNaN = float64_is_signaling_nan(b);
+ cIsQuietNaN = float64_is_quiet_nan(c);
+ cIsSignalingNaN = float64_is_signaling_nan(c);
+
+ if (aIsSignalingNaN | bIsSignalingNaN | cIsSignalingNaN) {
+ float_raise(float_flag_invalid STATUS_VAR);
+ }
+
+ which = pickNaNMulAdd(aIsQuietNaN, aIsSignalingNaN,
+ bIsQuietNaN, bIsSignalingNaN,
+ cIsQuietNaN, cIsSignalingNaN, infzero STATUS_VAR);
+
+ if (STATUS(default_nan_mode)) {
+ /* Note that this check is after pickNaNMulAdd so that function
+ * has an opportunity to set the Invalid flag.
+ */
+ return float64_default_nan;
+ }
+
+ switch (which) {
+ case 0:
+ return float64_maybe_silence_nan(a);
+ case 1:
+ return float64_maybe_silence_nan(b);
+ case 2:
+ return float64_maybe_silence_nan(c);
+ case 3:
+ default:
+ return float64_default_nan;
+ }
+}
+
+/*----------------------------------------------------------------------------
| Returns 1 if the extended double-precision floating-point value `a' is a
| quiet NaN; otherwise returns 0. This slightly differs from the same
| function for other types as floatx80 has an explicit bit.
