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From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: alex.bennee@linaro.org, david@redhat.com
Subject: [PATCH v2 11/28] softfloat: Adjust parts_uncanon_normal for floatx80
Date: Tue, 25 May 2021 08:06:49 -0700	[thread overview]
Message-ID: <20210525150706.294968-12-richard.henderson@linaro.org> (raw)
In-Reply-To: <20210525150706.294968-1-richard.henderson@linaro.org>

With floatx80_precision_x, the rounding happens across
the break between words.  Notice this case with

  frac_lsb = round_mask + 1 -> 0

and check the bits in frac_hi as needed.

In addition, since frac_shift == 0, we won't implicitly clear
round_mask via the right-shift, so explicitly clear those bits.
This fixes rounding for floatx80_precision_[sd].

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 fpu/softfloat-parts.c.inc | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
index b456c1c30c..8a7f22d6b5 100644
--- a/fpu/softfloat-parts.c.inc
+++ b/fpu/softfloat-parts.c.inc
@@ -156,7 +156,13 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
     switch (s->float_rounding_mode) {
     case float_round_nearest_even:
         overflow_norm = false;
-        inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1 ? frac_lsbm1 : 0);
+        if (N > 64 && frac_lsb == 0) {
+            inc = ((p->frac_hi & 1) || (p->frac_lo & round_mask) != frac_lsbm1
+                   ? frac_lsbm1 : 0);
+        } else {
+            inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
+                   ? frac_lsbm1 : 0);
+        }
         break;
     case float_round_ties_away:
         overflow_norm = false;
@@ -176,7 +182,11 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
         break;
     case float_round_to_odd:
         overflow_norm = true;
-        inc = p->frac_lo & frac_lsb ? 0 : round_mask;
+        if (N > 64 && frac_lsb == 0) {
+            inc = p->frac_hi & 1 ? 0 : round_mask;
+        } else {
+            inc = p->frac_lo & frac_lsb ? 0 : round_mask;
+        }
         break;
     default:
         g_assert_not_reached();
@@ -191,8 +201,8 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
                 p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
                 exp++;
             }
+            p->frac_lo &= ~round_mask;
         }
-        frac_shr(p, frac_shift);
 
         if (fmt->arm_althp) {
             /* ARM Alt HP eschews Inf and NaN for a wider exponent.  */
@@ -201,18 +211,21 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
                 flags = float_flag_invalid;
                 exp = exp_max;
                 frac_allones(p);
+                p->frac_lo &= ~round_mask;
             }
         } else if (unlikely(exp >= exp_max)) {
             flags |= float_flag_overflow | float_flag_inexact;
             if (overflow_norm) {
                 exp = exp_max - 1;
                 frac_allones(p);
+                p->frac_lo &= ~round_mask;
             } else {
                 p->cls = float_class_inf;
                 exp = exp_max;
                 frac_clear(p);
             }
         }
+        frac_shr(p, frac_shift);
     } else if (s->flush_to_zero) {
         flags |= float_flag_output_denormal;
         p->cls = float_class_zero;
@@ -232,17 +245,28 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
             /* Need to recompute round-to-even/round-to-odd. */
             switch (s->float_rounding_mode) {
             case float_round_nearest_even:
-                inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
-                       ? frac_lsbm1 : 0);
+                if (N > 64 && frac_lsb == 0) {
+                    inc = ((p->frac_hi & 1) ||
+                           (p->frac_lo & round_mask) != frac_lsbm1
+                           ? frac_lsbm1 : 0);
+                } else {
+                    inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
+                           ? frac_lsbm1 : 0);
+                }
                 break;
             case float_round_to_odd:
-                inc = p->frac_lo & frac_lsb ? 0 : round_mask;
+                if (N > 64 && frac_lsb == 0) {
+                    inc = p->frac_hi & 1 ? 0 : round_mask;
+                } else {
+                    inc = p->frac_lo & frac_lsb ? 0 : round_mask;
+                }
                 break;
             default:
                 break;
             }
             flags |= float_flag_inexact;
             frac_addi(p, p, inc);
+            p->frac_lo &= ~round_mask;
         }
 
         exp = (p->frac_hi & DECOMPOSED_IMPLICIT_BIT) != 0;
-- 
2.25.1



  parent reply	other threads:[~2021-05-25 16:11 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25 15:06 [PATCH v2 00/28] Convert floatx80 and float128 to FloatParts Richard Henderson
2021-05-25 15:06 ` [PATCH v2 01/28] softfloat: Move round_to_uint_and_pack to softfloat-parts.c.inc Richard Henderson
2021-06-02 11:12   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 02/28] softfloat: Move int_to_float " Richard Henderson
2021-05-26 13:34   ` David Hildenbrand
2021-06-02 11:14   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 03/28] softfloat: Move uint_to_float " Richard Henderson
2021-05-26 13:36   ` David Hildenbrand
2021-06-02 11:31   ` Alex Bennée
2021-06-02 16:28     ` Richard Henderson
2021-05-25 15:06 ` [PATCH v2 04/28] softfloat: Move minmax_flags " Richard Henderson
2021-05-26 13:45   ` David Hildenbrand
2021-06-02 20:36   ` Alex Bennée
2021-06-02 22:23     ` Richard Henderson
2021-06-02 22:29   ` Richard Henderson
2021-05-25 15:06 ` [PATCH v2 05/28] softfloat: Move compare_floats " Richard Henderson
2021-06-03  9:00   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 06/28] softfloat: Move scalbn_decomposed " Richard Henderson
2021-06-03  9:01   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 07/28] softfloat: Move sqrt_float " Richard Henderson
2021-06-03  9:17   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 08/28] softfloat: Split out parts_uncanon_normal Richard Henderson
2021-06-03  9:22   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 09/28] softfloat: Reduce FloatFmt Richard Henderson
2021-06-03  9:23   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 10/28] softfloat: Introduce Floatx80RoundPrec Richard Henderson
2021-06-03  9:26   ` Alex Bennée
2021-05-25 15:06 ` Richard Henderson [this message]
2021-06-03 11:58   ` [PATCH v2 11/28] softfloat: Adjust parts_uncanon_normal for floatx80 Alex Bennée
2021-05-25 15:06 ` [PATCH v2 12/28] tests/fp/fp-test: Reverse order of floatx80 precision tests Richard Henderson
2021-05-25 15:06 ` [PATCH v2 13/28] softfloat: Convert floatx80_add/sub to FloatParts Richard Henderson
2021-06-03 14:23   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 14/28] softfloat: Convert floatx80_mul " Richard Henderson
2021-06-03 14:23   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 15/28] softfloat: Convert floatx80_div " Richard Henderson
2021-06-03 14:23   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 16/28] softfloat: Convert floatx80_sqrt " Richard Henderson
2021-06-03 14:24   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 17/28] softfloat: Convert floatx80_round " Richard Henderson
2021-06-03 14:25   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 18/28] softfloat: Convert floatx80_round_to_int " Richard Henderson
2021-06-03 14:26   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 19/28] softfloat: Convert integer to floatx80 " Richard Henderson
2021-06-03 14:26   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 20/28] softfloat: Convert floatx80 float conversions " Richard Henderson
2021-06-03 14:26   ` Alex Bennée
2021-05-25 15:06 ` [PATCH v2 21/28] softfloat: Convert floatx80 to integer " Richard Henderson
2021-06-03 14:27   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 22/28] softfloat: Convert floatx80_scalbn " Richard Henderson
2021-06-03 14:34   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 23/28] softfloat: Convert floatx80 compare " Richard Henderson
2021-06-03 14:34   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 24/28] softfloat: Convert float32_exp2 " Richard Henderson
2021-06-03 14:44   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 25/28] softfloat: Move floatN_log2 to softfloat-parts.c.inc Richard Henderson
2021-06-02 15:28   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 26/28] softfloat: Convert modrem operations to FloatParts Richard Henderson
2021-06-03 14:48   ` Alex Bennée
2021-05-25 15:07 ` [PATCH v2 27/28] tests/fp: Enable more tests Richard Henderson
2021-05-25 15:07 ` [PATCH v2 28/28] softfloat: Use hard-float for {u}int64_to_float{32, 64} Richard Henderson
2021-06-03 14:57   ` [PATCH v2 28/28] softfloat: Use hard-float for {u}int64_to_float{32,64} Alex Bennée
2021-05-25 16:51 ` [PATCH v2 00/28] Convert floatx80 and float128 to FloatParts no-reply

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