fpu: Split scalbn from partsN(muladd_scalbn)

Handle the scaling separately with parts64_scalbn.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
index 028c2daa2730620bb25d3b09ee301b7fc054153f..b8baaf1e76d65c7e260e25d5595bb0c9bcbde2ea 100644 (file)
--- a/fpu/softfloat-parts.c.inc
+++ b/fpu/softfloat-parts.c.inc
@@ -669,17 +669,19 @@ static FloatPartsN *partsN(mul)(FloatPartsN *a, FloatPartsN *b,
  * `b' then adding 'c', with no intermediate rounding step after the
  * multiplication. The operation is performed according to the
  * IEC/IEEE Standard for Binary Floating-Point Arithmetic 754-2008.
- * The flags argument allows the caller to select negation of the
- * addend, the intermediate product, or the final result. (The
- * difference between this and having the caller do a separate
- * negation is that negating externally will flip the sign bit on NaNs.)
+ * The flags argument allows the caller to select negation of the addend
+ * or the intermediate product. (The difference between this and having
+ * the caller do a separate negation is that negating externally will
+ * flip the sign bit on NaNs.) Note that float_muladd_negate_result
+ * is not applied here, and should be handled separately after rounding
+ * chooses the final sign of 0.0.
  *
  * Requires A and C extracted into a double-sized structure to provide the
  * extra space for the widening multiply.
  */
-static FloatPartsN *partsN(muladd_scalbn)(FloatPartsN *a, FloatPartsN *b,
-                                          FloatPartsN *c, int scale,
-                                          int flags, float_status *s)
+static FloatPartsN *partsN(muladd)(FloatPartsN *a, FloatPartsN *b,
+                                   FloatPartsN *c,
+                                   int flags, float_status *s)
 {
     int ab_mask, abc_mask;
     FloatPartsW p_widen, c_widen;
@@ -725,7 +727,7 @@ static FloatPartsN *partsN(muladd_scalbn)(FloatPartsN *a, FloatPartsN *b,
         g_assert(ab_mask & float_cmask_zero);
         if (is_anynorm(c->cls)) {
             *a = *c;
-            goto return_normal;
+            goto finish_sign;
         }
         if (c->cls == float_class_zero) {
             if (flags & float_muladd_suppress_add_product_zero) {
@@ -770,8 +772,6 @@ static FloatPartsN *partsN(muladd_scalbn)(FloatPartsN *a, FloatPartsN *b,
     a->sign = p_widen.sign;
     a->exp = p_widen.exp;
 
- return_normal:
-    a->exp += scale;
  finish_sign:
     /*
      * All result types except for "return the default NaN

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 0a8da13e010364fb7d4abc4129d245829817ec8c..962528cb73f0de2893eda682118b51936a2560c4 100644 (file)
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1907,11 +1907,14 @@ float16_muladd_scalbn(float16 a, float16 b, float16 c,
     FloatParts64 pa = float16_unpack_canonical(a, status);
     FloatParts64 pb = float16_unpack_canonical(b, status);
     FloatParts64 pc = float16_unpack_canonical(c, status);
-    FloatParts64 *pr =
-        parts64_muladd_scalbn(&pa, &pb, &pc, scale, flags, status);
+    FloatParts64 *pr = parts64_muladd(&pa, &pb, &pc, flags, status);
 
-    /* Round before applying negate result. */
+    /* Before rounding, scale. */
+    if (scale) {
+        parts64_scalbn(pr, scale, status);
+    }
     parts64_uncanon(pr, status, &float16_params, false);
+    /* After rounding, apply negate result, especially for -0.0. */
     if ((flags & float_muladd_negate_result) && !is_nan(pr->cls)) {
         pr->sign ^= 1;
     }
@@ -1931,10 +1934,14 @@ float32_muladd_scalbn(float32 a, float32 b, float32 c,
     FloatParts64 pa = float32_unpack_canonical(a, status);
     FloatParts64 pb = float32_unpack_canonical(b, status);
     FloatParts64 pc = float32_unpack_canonical(c, status);
-    FloatParts64 *pr = parts64_muladd_scalbn(&pa, &pb, &pc, scale, flags, status);
+    FloatParts64 *pr = parts64_muladd(&pa, &pb, &pc, flags, status);
 
-    /* Round before applying negate result. */
+    /* Before rounding, scale. */
+    if (scale) {
+        parts64_scalbn(pr, scale, status);
+    }
     parts64_uncanon(pr, status, &float32_params, false);
+    /* After rounding, apply negate result, especially for -0.0. */
     if ((flags & float_muladd_negate_result) && !is_nan(pr->cls)) {
         pr->sign ^= 1;
     }
@@ -1948,10 +1955,14 @@ float64_muladd_scalbn(float64 a, float64 b, float64 c,
     FloatParts64 pa = float64_unpack_canonical(a, status);
     FloatParts64 pb = float64_unpack_canonical(b, status);
     FloatParts64 pc = float64_unpack_canonical(c, status);
-    FloatParts64 *pr = parts64_muladd_scalbn(&pa, &pb, &pc, scale, flags, status);
+    FloatParts64 *pr = parts64_muladd(&pa, &pb, &pc, flags, status);
 
-    /* Round before applying negate result. */
+    /* Before rounding, scale. */
+    if (scale) {
+        parts64_scalbn(pr, scale, status);
+    }
     parts64_uncanon(pr, status, &float64_params, false);
+    /* After rounding, apply negate result, especially for -0.0. */
     if ((flags & float_muladd_negate_result) && !is_nan(pr->cls)) {
         pr->sign ^= 1;
     }
@@ -2105,7 +2116,7 @@ float64 float64r32_muladd(float64 a, float64 b, float64 c,
     FloatParts64 pa = float64_unpack_canonical(a, status);
     FloatParts64 pb = float64_unpack_canonical(b, status);
     FloatParts64 pc = float64_unpack_canonical(c, status);
-    FloatParts64 *pr = parts64_muladd_scalbn(&pa, &pb, &pc, 0, flags, status);
+    FloatParts64 *pr = parts64_muladd(&pa, &pb, &pc, flags, status);
 
     /* Round before applying negate result. */
     parts64_uncanon(pr, status, &float32_params, false);
@@ -2121,7 +2132,7 @@ bfloat16 QEMU_FLATTEN bfloat16_muladd(bfloat16 a, bfloat16 b, bfloat16 c,
     FloatParts64 pa = bfloat16_unpack_canonical(a, status);
     FloatParts64 pb = bfloat16_unpack_canonical(b, status);
     FloatParts64 pc = bfloat16_unpack_canonical(c, status);
-    FloatParts64 *pr = parts64_muladd_scalbn(&pa, &pb, &pc, 0, flags, status);
+    FloatParts64 *pr = parts64_muladd(&pa, &pb, &pc, flags, status);
 
     /* Round before applying negate result. */
     parts64_uncanon(pr, status, &bfloat16_params, false);
@@ -2137,7 +2148,7 @@ float128 QEMU_FLATTEN float128_muladd(float128 a, float128 b, float128 c,
     FloatParts128 pa = float128_unpack_canonical(a, status);
     FloatParts128 pb = float128_unpack_canonical(b, status);
     FloatParts128 pc = float128_unpack_canonical(c, status);
-    FloatParts128 *pr = parts128_muladd_scalbn(&pa, &pb, &pc, 0, flags, status);
+    FloatParts128 *pr = parts128_muladd(&pa, &pb, &pc, flags, status);
 
     /* Round before applying negate result. */
     parts128_uncanon(pr, status, &float128_params, false);
@@ -5116,7 +5127,7 @@ float32 float32_exp2(float32 a, float_status *status)
     rp = float64_unpack_canonical(float64_one, status);
     for (int i = 0; i < 15; i++) {
         tp = float64_unpack_canonical(float32_exp2_coefficients[i], status);
-        rp = *parts64_muladd_scalbn(&tp, &xnp, &rp, 0, 0, status);
+        rp = *parts64_muladd(&tp, &xnp, &rp, 0, status);
         xnp = *parts64_mul(&xnp, &xp, status);
     }
 
@@ -5196,8 +5207,8 @@ static void parts_s390_divide_to_integer(FloatParts64 *a, FloatParts64 *b,
 
         /* Compute precise remainder */
         r_precise_buf = *b;
-        r_precise = parts64_muladd_scalbn(&r_precise_buf, n, a, 0,
-                                          float_muladd_negate_product, status);
+        r_precise = parts64_muladd(&r_precise_buf, n, a,
+                                   float_muladd_negate_product, status);
 
         /* Round remainder to the target format */
         *r = *r_precise;