[Qemu-devel] [PATCH v2 09/14] hardfloat: support float32/64 multiplication

["Emilio G. Cota" <cota@braap.org>]

Performance results for fp-bench run under aarch64-linux-user
on an Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz host:

- before:
mul-single: 88.37 MFlops
mul-double: 85.55 MFlops

- after:
mul-single: 115.06 MFlops
mul-double: 124.67 MFlops

- w/ both using float32/64_is_normal etc.:
mul-single: 113.49 MFlops
mul-double: 113.46 MFlops

- w/ both using fpclassify etc.:
mul-single: 105.70 MFlops
mul-double: 127.69 MFlops

Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 fpu/softfloat.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 4 deletions(-)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index e0ab0ca..9739a86 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1044,8 +1044,8 @@ float16 __attribute__((flatten)) float16_mul(float16 a, float16 b,
     return float16_round_pack_canonical(pr, status);
 }
 
-float32 __attribute__((flatten)) float32_mul(float32 a, float32 b,
-                                             float_status *status)
+static float32 __attribute__((flatten, noinline))
+soft_float32_mul(float32 a, float32 b, float_status *status)
 {
     FloatParts pa = float32_unpack_canonical(a, status);
     FloatParts pb = float32_unpack_canonical(b, status);
@@ -1054,8 +1054,8 @@ float32 __attribute__((flatten)) float32_mul(float32 a, float32 b,
     return float32_round_pack_canonical(pr, status);
 }
 
-float64 __attribute__((flatten)) float64_mul(float64 a, float64 b,
-                                             float_status *status)
+static float64 __attribute__((flatten, noinline))
+soft_float64_mul(float64 a, float64 b, float_status *status)
 {
     FloatParts pa = float64_unpack_canonical(a, status);
     FloatParts pb = float64_unpack_canonical(b, status);
@@ -1064,6 +1064,75 @@ float64 __attribute__((flatten)) float64_mul(float64 a, float64 b,
     return float64_round_pack_canonical(pr, status);
 }
 
+#define GEN_FPU_MUL(name, soft_t, host_t, host_abs_func, min_normal)    \
+    soft_t name(soft_t a, soft_t b, float_status *s)                    \
+    {                                                                   \
+        soft_t ## _input_flush2(&a, &b, s);                             \
+        if (likely((soft_t ## _is_normal(a) || soft_t ## _is_zero(a)) && \
+                   (soft_t ## _is_normal(b) || soft_t ## _is_zero(b)) && \
+                   s->float_exception_flags & float_flag_inexact &&     \
+                   s->float_rounding_mode == float_round_nearest_even)) { \
+            if (soft_t ## _is_zero(a) || soft_t ## _is_zero(b)) {       \
+                bool signbit = soft_t ## _is_neg(a) ^ soft_t ## _is_neg(b); \
+                                                                        \
+                return soft_t ## _set_sign(soft_t ## _zero, signbit);   \
+            } else {                                                    \
+                host_t ha = soft_t ## _to_ ## host_t(a);                \
+                host_t hb = soft_t ## _to_ ## host_t(b);                \
+                host_t hr = ha * hb;                                    \
+                soft_t r = host_t ## _to_ ## soft_t(hr);                \
+                                                                        \
+                if (unlikely(soft_t ## _is_infinity(r))) {              \
+                    s->float_exception_flags |= float_flag_overflow;    \
+                } else if (unlikely(host_abs_func(hr) <= min_normal)) { \
+                    goto soft;                                          \
+                }                                                       \
+                return r;                                               \
+            }                                                           \
+        }                                                               \
+    soft:                                                               \
+        return soft_ ## soft_t ## _mul(a, b, s);                        \
+    }
+
+GEN_FPU_MUL(float32_mul, float32, float, fabsf, FLT_MIN)
+#undef GEN_FPU_MUL
+
+#define GEN_FPU_MUL(name, soft_t, host_t, host_abs_func, min_normal)    \
+    soft_t name(soft_t a, soft_t b, float_status *s)                    \
+    {                                                                   \
+        host_t ha, hb;                                                  \
+                                                                        \
+        soft_t ## _input_flush2(&a, &b, s);                             \
+        ha = soft_t ## _to_ ## host_t(a);                               \
+        hb = soft_t ## _to_ ## host_t(b);                               \
+        if (likely((fpclassify(ha) == FP_NORMAL ||                      \
+                    fpclassify(ha) == FP_ZERO) &&                       \
+                   (fpclassify(hb) == FP_NORMAL ||                      \
+                    fpclassify(hb) == FP_ZERO) &&                       \
+                   s->float_exception_flags & float_flag_inexact &&     \
+                   s->float_rounding_mode == float_round_nearest_even)) { \
+            if (soft_t ## _is_zero(a) || soft_t ## _is_zero(b)) {       \
+                bool signbit = soft_t ## _is_neg(a) ^ soft_t ## _is_neg(b); \
+                                                                        \
+                return soft_t ## _set_sign(soft_t ## _zero, signbit);   \
+            } else {                                                    \
+                host_t hr = ha * hb;                                    \
+                                                                        \
+                if (unlikely(isinf(hr))) {                              \
+                    s->float_exception_flags |= float_flag_overflow;    \
+                } else if (unlikely(host_abs_func(hr) <= min_normal)) { \
+                    goto soft;                                          \
+                }                                                       \
+                return host_t ## _to_ ## soft_t(hr);                    \
+            }                                                           \
+        }                                                               \
+    soft:                                                               \
+        return soft_ ## soft_t ## _mul(a, b, s);                        \
+    }
+
+GEN_FPU_MUL(float64_mul, float64, double, fabs, DBL_MIN)
+#undef GEN_FPU_MUL
+
 /*
  * Returns the result of multiplying the floating-point values `a' and
  * `b' then adding 'c', with no intermediate rounding step after the
-- 
2.7.4