From d73ed2601b7c3c93c3529149a3d7f7b6177900a8 Mon Sep 17 00:00:00 2001
From: Joseph Myers <josmyers@redhat.com>
Date: Tue, 27 Aug 2024 12:38:01 +0000
Subject: More thoroughly test underflow / errno in tst-strtod-round

Add tests of underflow in tst-strtod-round, and thus also test for
errno being unchanged when there is neither overflow nor underflow.
The errno setting before the function call to test for being unchanged
is adjusted to set errno to 12345 instead of 0, so that any bugs where
strtod sets errno to 0 would be detected.

This doesn't add any new test inputs for tst-strtod-round, and in
particular doesn't cover the edge cases of underflow the way
tst-strtod-underflow does (none of the existing test inputs for
tst-strtod-round actually exercise cases that have underflow with
before-rounding tininess detection but not with after-rounding
tininess detection), but at least it provides some coverage (as per
the recent discussions) that ordinary non-overflowing non-underflowing
inputs to these functions do not set errno.

Tested for x86_64.
---
 stdlib/gen-tst-strtod-round.c | 43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

(limited to 'stdlib/gen-tst-strtod-round.c')

diff --git a/stdlib/gen-tst-strtod-round.c b/stdlib/gen-tst-strtod-round.c
index e48bf4d6ea..7ce735f81d 100644
--- a/stdlib/gen-tst-strtod-round.c
+++ b/stdlib/gen-tst-strtod-round.c
@@ -46,6 +46,7 @@ static int
 string_to_fp (mpfr_t f, const char *s, mpfr_rnd_t rnd)
 {
   mpfr_clear_overflow ();
+  mpfr_clear_underflow ();
 #ifdef WORKAROUND
   mpfr_t f2;
   mpfr_init2 (f2, 100000);
@@ -53,12 +54,16 @@ string_to_fp (mpfr_t f, const char *s, mpfr_rnd_t rnd)
   int r = mpfr_set (f, f2, rnd);
   r |= mpfr_subnormalize (f, r, rnd);
   mpfr_clear (f2);
-  return r0 | r;
+  r |= r0;
 #else
   int r = mpfr_strtofr (f, s, NULL, 0, rnd);
   r |= mpfr_subnormalize (f, r, rnd);
-  return r;
 #endif
+  if (r == 0)
+    /* The MPFR underflow flag is set for exact subnormal results,
+       which is not wanted here.  */
+    mpfr_clear_underflow ();
+  return r;
 }
 
 void
@@ -70,6 +75,21 @@ print_fp (FILE *fout, mpfr_t f, const char *suffix)
     mpfr_fprintf (fout, "\t%Ra%s", f, suffix);
 }
 
+static const char *
+suffix_to_print (bool overflow, bool underflow, bool underflow_before_rounding,
+		 bool with_comma)
+{
+  if (overflow)
+    return with_comma ? ", true, false,\n" : ", true, false";
+  if (underflow)
+    return with_comma ? ", false, true,\n" : ", false, true";
+  if (underflow_before_rounding)
+    return (with_comma
+	    ? ", false, !TININESS_AFTER_ROUNDING,\n"
+	    : ", false, !TININESS_AFTER_ROUNDING");
+  return with_comma ? ", false, false,\n" : ", false, false";
+}
+
 static void
 round_str (FILE *fout, const char *s, int prec, int emin, int emax,
 	   bool ibm_ld)
@@ -80,8 +100,11 @@ round_str (FILE *fout, const char *s, int prec, int emin, int emax,
   mpfr_set_emin (emin);
   mpfr_set_emax (emax);
   mpfr_init (f);
+  string_to_fp (f, s, MPFR_RNDZ);
+  bool underflow_before_rounding = mpfr_underflow_p () != 0;
   int r = string_to_fp (f, s, MPFR_RNDD);
   bool overflow = mpfr_overflow_p () != 0;
+  bool underflow = mpfr_underflow_p () != 0;
   if (ibm_ld)
     {
       assert (prec == 106 && emin == -1073 && emax == 1024);
@@ -97,19 +120,27 @@ round_str (FILE *fout, const char *s, int prec, int emin, int emax,
 	}
     }
   mpfr_fprintf (fout, "\t%s,\n", r ? "false" : "true");
-  print_fp (fout, f, overflow ? ", true,\n" : ", false,\n");
+  print_fp (fout, f,
+	    suffix_to_print (overflow, underflow, underflow_before_rounding,
+			     true));
   string_to_fp (f, s, MPFR_RNDN);
   overflow = (mpfr_overflow_p () != 0
 	      || (ibm_ld && mpfr_cmpabs (f, max_value) > 0));
-  print_fp (fout, f, overflow ? ", true,\n" : ", false,\n");
+  print_fp (fout, f,
+	    suffix_to_print (overflow, underflow, underflow_before_rounding,
+			     true));
   string_to_fp (f, s, MPFR_RNDZ);
   overflow = (mpfr_overflow_p () != 0
 	      || (ibm_ld && mpfr_cmpabs (f, max_value) > 0));
-  print_fp (fout, f, overflow ? ", true,\n" : ", false,\n");
+  print_fp (fout, f,
+	    suffix_to_print (overflow, underflow, underflow_before_rounding,
+			     true));
   string_to_fp (f, s, MPFR_RNDU);
   overflow = (mpfr_overflow_p () != 0
 	      || (ibm_ld && mpfr_cmpabs (f, max_value) > 0));
-  print_fp (fout, f, overflow ? ", true" : ", false");
+  print_fp (fout, f,
+	    suffix_to_print (overflow, underflow, underflow_before_rounding,
+			     false));
   mpfr_clear (f);
   if (ibm_ld)
     mpfr_clear (max_value);
-- 
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