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.

(cherry picked from commit d73ed2601b)

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);

stdlib/tst-strtod-round-skeleton.c

@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <math-tests.h>
+#include <tininess.h>
 
 #include "tst-strtod.h"
 
@@ -139,16 +140,26 @@
    gen-tst-strtod-round utility to select the appropriately
    rounded long double value for a given format.  */
 #define TEST(s,							\
-	     fx, fd, fdo, fn, fno, fz, fzo, fu, fuo,		\
-	     dx, dd, ddo, dn, dno, dz, dzo, du, duo,		\
-	     ld64ix, ld64id, ld64ido, ld64in, ld64ino,		\
-	     ld64iz, ld64izo, ld64iu, ld64iuo,			\
-	     ld64mx, ld64md, ld64mdo, ld64mn, ld64mno,		\
-	     ld64mz, ld64mzo, ld64mu, ld64muo,			\
-	     ld106x, ld106d, ld106do, ld106n, ld106no,		\
-	     ld106z, ld106zo, ld106u, ld106uo,			\
-	     ld113x, ld113d, ld113do, ld113n, ld113no,		\
-	     ld113z, ld113zo, ld113u, ld113uo)			\
+	     fx, fd, fdo, fdu, fn, fno, fnu,			\
+	     fz, fzo, fzu, fu, fuo, fuu,			\
+	     dx, dd, ddo, ddu, dn, dno, dnu,			\
+	     dz, dzo, dzu, du, duo, duu,			\
+	     ld64ix, ld64id, ld64ido, ld64idu,			\
+	     ld64in, ld64ino, ld64inu,				\
+	     ld64iz, ld64izo, ld64izu,				\
+	     ld64iu, ld64iuo, ld64iuu,				\
+	     ld64mx, ld64md, ld64mdo, ld64mdu,			\
+	     ld64mn, ld64mno, ld64mnu,				\
+	     ld64mz, ld64mzo, ld64mzu,				\
+	     ld64mu, ld64muo, ld64muu,				\
+	     ld106x, ld106d, ld106do, ld106du,			\
+	     ld106n, ld106no, ld106nu,				\
+	     ld106z, ld106zo, ld106zu,				\
+	     ld106u, ld106uo, ld106uu,				\
+	     ld113x, ld113d, ld113do, ld113du,			\
+	     ld113n, ld113no, ld113nu,				\
+	     ld113z, ld113zo, ld113zu,				\
+	     ld113u, ld113uo, ld113uu)				\
   {								\
     L_ (s),							\
     { XNTRY (fx, dx, ld64ix, ld64mx, ld106x, ld113x) },		\
@@ -163,6 +174,12 @@
     { XNTRY (fdo, ddo, ld64ido, ld64mdo, ld106do, ld113do) },	\
     { XNTRY (fzo, dzo, ld64izo, ld64mzo, ld106zo, ld113zo) },	\
     { XNTRY (fuo, duo, ld64iuo, ld64muo, ld106uo, ld113uo) }	\
+    },								\
+    {								\
+    { XNTRY (fnu, dnu, ld64inu, ld64mnu, ld106nu, ld113nu) },	\
+    { XNTRY (fdu, ddu, ld64idu, ld64mdu, ld106du, ld113du) },	\
+    { XNTRY (fzu, dzu, ld64izu, ld64mzu, ld106zu, ld113zu) },	\
+    { XNTRY (fuu, duu, ld64iuu, ld64muu, ld106uu, ld113uu) }	\
     }								\
   }
 
@@ -181,11 +198,17 @@ struct test_overflow
   STRUCT_FOREACH_FLOAT_BOOL
   };
 
+struct test_underflow
+  {
+  STRUCT_FOREACH_FLOAT_BOOL
+  };
+
 struct test {
   const CHAR *s;
   struct test_exactness exact;
   struct test_results r[4];
   struct test_overflow o[4];
+  struct test_underflow u[4];
 };
 
 /* Include the generated test data.  */
@@ -203,10 +226,14 @@ struct test {
 # define FE_OVERFLOW 0
 #endif
 
+#ifndef FE_UNDERFLOW
+# define FE_UNDERFLOW 0
+#endif
+
 #define GEN_ONE_TEST(FSUF, FTYPE, FTOSTR, LSUF, CSUF)		\
 {								\
   feclearexcept (FE_ALL_EXCEPT);				\
-  errno = 0;							\
+  errno = 12345;						\
   FTYPE f = STRTO (FSUF) (s, NULL);				\
   int new_errno = errno;					\
   if (f != expected->FSUF					\
@@ -265,6 +292,40 @@ struct test {
 		  s, new_errno, ERANGE);			\
 	  result = 1;						\
 	}							\
+      if (FE_UNDERFLOW != 0)					\
+	{							\
+	  bool underflow_raised					\
+	    = fetestexcept (FE_UNDERFLOW) != 0;			\
+	  if (underflow_raised != underflow->FSUF)		\
+	    {							\
+	      printf (FNPFXS "to" #FSUF				\
+		      " (" STRM ") underflow %d "		\
+		      "not %d\n", s, underflow_raised,		\
+		      underflow->FSUF);				\
+	      if (EXCEPTION_TESTS (FTYPE))			\
+		result = 1;					\
+	      else						\
+		printf ("ignoring this exception error\n");	\
+	    }							\
+	}							\
+      if (underflow->FSUF && new_errno != ERANGE)		\
+	{							\
+	  printf (FNPFXS "to" #FSUF				\
+		  " (" STRM ") left errno == %d,"		\
+		  " not %d (ERANGE)\n",				\
+		  s, new_errno, ERANGE);			\
+	  result = 1;						\
+	}							\
+      if (!overflow->FSUF					\
+	  && !underflow->FSUF					\
+	  && new_errno != 12345)				\
+	{							\
+	  printf (FNPFXS "to" #FSUF				\
+		  " (" STRM ") set errno == %d,"		\
+		  " should be unchanged\n",			\
+		  s, new_errno);				\
+	  result = 1;						\
+	}							\
     }								\
 }
 
@@ -272,6 +333,7 @@ static int
 test_in_one_mode (const CHAR *s, const struct test_results *expected,
 		    const struct test_exactness *exact,
 		    const struct test_overflow *overflow,
+		    const struct test_underflow *underflow,
 		    const char *mode_name, int rnd_mode)
 {
   int result = 0;
@@ -307,6 +369,7 @@ do_test (void)
     {
       result |= test_in_one_mode (tests[i].s, &tests[i].r[modes[0].rnd_i],
 				  &tests[i].exact, &tests[i].o[modes[0].rnd_i],
+				  &tests[i].u[modes[0].rnd_i],
 				  modes[0].mode_name, modes[0].rnd_mode);
       for (const struct fetestmodes *m = &modes[1]; m->mode_name != NULL; m++)
 	{
@@ -314,7 +377,9 @@ do_test (void)
 	    {
 	      result |= test_in_one_mode (tests[i].s, &tests[i].r[m->rnd_i],
 					  &tests[i].exact,
-					  &tests[i].o[m->rnd_i], m->mode_name,
+					  &tests[i].o[m->rnd_i],
+					  &tests[i].u[m->rnd_i],
+					  m->mode_name,
 					  m->rnd_mode);
 	      fesetround (save_round_mode);
 	    }