[PATCH v2] stdlib/strfrom: Change -NAN test to multiple possible results (bug 29501)

[Letu Ren <fantasquex@gmail.com>]

According to the specification of ISO/IEC TS 18661-1:2014,

The strfromd, strfromf, and strfroml functions are equivalent to
snprintf(s, n, format, fp) (7.21.6.5), except the format string contains only
the character %, an optional precision that does not contain an asterisk *, and
one of the conversion specifiers a, A, e, E, f, F, g, or G, which applies to
the type (double, float, or long double) indicated by the function suffix
(rather than  by a length modifier). Use of these functions with any other 20
format string results in undefined behavior.

strfromf will convert the arguement with type float to double first.

According to the latest version of IEEE754 which is published in 2019,

Conversion of a quiet NaN from a narrower format to a wider format in the same
radix, and then back to the same narrower format, should not change the quiet
NaN payload in any way except to make it canonical.

When either an input or result is a NaN, this standard does not interpret the
sign of a NaN. However, operations on bit strings—copy, negate, abs,
copySign—specify the sign bit of a NaN result, sometimes based upon the sign
bit of a NaN operand. The logical predicates totalOrder and isSignMinus are
also affected by the sign bit of a NaN operand. For all other operations, this
standard does not specify the sign bit of a NaN result, even when there is only
one input NaN, or when the NaN is produced from an invalid operation.

converting NAN or -NAN with type float to double doesn't need to keep
the signbit. As a result, this test case isn't mandatory.

The problem is that according to RISC-V ISA manual in chapter 11.3 of
riscv-isa-20191213,

Except when otherwise stated, if the result of a floating-point operation is
NaN, it is the canonical NaN. The canonical NaN has a positive sign and all
significand bits clear except the MSB, a.k.a. the quiet bit. For
single-precision floating-point, this corresponds to the pattern 0x7fc00000.

which means that conversion -NAN from float to double won't keep the signbit.

This patch changes the original -NAN test case to NAN and adds a special
test which accepts two possible results to test -NAN.

This patch has been tested on x86_64 and riscv64. Except some tests
fails on riscv64 due to timeout, all tests pass.

Signed-off-by: Letu Ren <fantasquex@gmail.com>
---
 stdlib/tst-strfrom-locale.c |  6 +++++-
 stdlib/tst-strfrom.c        |  6 +++++-
 stdlib/tst-strfrom.h        | 26 ++++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/stdlib/tst-strfrom-locale.c b/stdlib/tst-strfrom-locale.c
index 85907c0ce1..1b0418c20e 100644
--- a/stdlib/tst-strfrom-locale.c
+++ b/stdlib/tst-strfrom-locale.c
@@ -37,10 +37,14 @@ static const struct test tests[] = {
   TEST ("5,900000e-16", "%e", 50, 12, 5.9e-16),
   TEST ("1,234500e+20", "%e", 50, 12, 12.345e19),
   TEST ("1,000000e+05", "%e", 50, 12, 1e5),
-  TEST ("-NAN", "%G", 50, 4, -NAN_),
+  TEST ("NAN", "%G", 50, 3, NAN_),
   TEST ("-inf", "%g", 50, 4, -INF),
   TEST ("inf", "%g", 50, 3, INF)
 };
+/* Tests with multiple possible results.  */
+static const struct sptest sptests[] = {
+  SPTEST ("-NAN", "NAN", "%G", 50, 4, 3, -NAN_)
+};
 /* Tests with buffer size small.  */
 static const struct test stest[] = {
   TEST ("1234", "%g", 5, 7, 12345.345),
diff --git a/stdlib/tst-strfrom.c b/stdlib/tst-strfrom.c
index 3a447eac12..3186db86fd 100644
--- a/stdlib/tst-strfrom.c
+++ b/stdlib/tst-strfrom.c
@@ -37,10 +37,14 @@ static const struct test tests[] = {
   TEST ("5.900000e-16", "%e", 50, 12, 5.9e-16),
   TEST ("1.234500e+20", "%e", 50, 12, 12.345e19),
   TEST ("1.000000e+05", "%e", 50, 12, 1e5),
-  TEST ("-NAN", "%G", 50, 4, -NAN_),
+  TEST ("NAN", "%G", 50, 3, NAN_),
   TEST ("-inf", "%g", 50, 4, -INF),
   TEST ("inf", "%g", 50, 3, INF)
 };
+/* Tests with multiple possible results.  */
+static const struct sptest sptests[] = {
+  SPTEST ("-NAN", "NAN", "%G", 50, 4, 3, -NAN_)
+};
 /* Tests with buffer size small.  */
 static const struct test stest[] = {
   TEST ("1234", "%g", 5, 7, 12345.345),
diff --git a/stdlib/tst-strfrom.h b/stdlib/tst-strfrom.h
index 2820a580c2..e80027fde9 100644
--- a/stdlib/tst-strfrom.h
+++ b/stdlib/tst-strfrom.h
@@ -59,6 +59,20 @@ struct test {
   {								\
     s, fmt, size, rc, { GEN_TEST_STRTOD_FOREACH (ENTRY, val) }	\
   }
+/* Tests with multiple possible results.  */
+struct sptest {
+  const char *s0;
+  const char *s1;
+  const char *fmt;
+  int size;
+  int rc0;
+  int rc1;
+  struct test_input t;
+};
+#define SPTEST(s0, s1, fmt, size, rc0, rc1, val)				\
+  {								\
+    s0, s1, fmt, size, rc0, rc1, { GEN_TEST_STRTOD_FOREACH (ENTRY, val) }	\
+  }
 /* Hexadecimal tests.  */
 struct htests
 {
@@ -100,6 +114,18 @@ test_ ## FSUF (void)							\
 	  status++;							\
 	}								\
     }									\
+  for (i = 0; i < sizeof (sptests) / sizeof (sptests[0]); i++)		\
+    {									\
+      rc = FTOSTR (buf, sptests[i].size, sptests[i].fmt, sptests[i].t.FSUF);	\
+      rc1 = (strcmp (buf, sptests[i].s0) != 0) || (rc != sptests[i].rc0);	\
+      rc1 &= (strcmp (buf, sptests[i].s1) != 0) || (rc != sptests[i].rc1);	\
+      if (rc1)								\
+	{								\
+	  printf (#FTOSTR ": got %s (%d), expected %s (%d) or %s (%d)\n",		\
+		  buf, rc, sptests[i].s0, sptests[i].rc0, sptests[i].s1, sptests[i].rc1); \
+	  status++;							\
+	}								\
+    }									\
   for (i = 0; i < sizeof (htest) / sizeof (htest[0]); i++)		\
     {									\
       rc = FTOSTR (buf, 50, htest[i].fmt, htest[i].t.FSUF);		\
-- 
2.37.3