(Updated) Work around bug in gcc 2.95.2 on hppa targets

Message-Id: <200204230034.UAA01134@mailhub2.stratus.com>

p4raw-id: //depot/perl@16092

1 files changed, 90 insertions, 0 deletions

diff --git a/hints/t001.c b/hints/t001.c
new file mode 100644
index 0000000000..51fdefda84
--- /dev/null
+++ b/hints/t001.c
@@ -0,0 +1,90 @@
+/* Beginning of modification history */
+/* Written 02-04-10 by Paul Green (Paul.Green@stratus.com) */
+/* End of modification history */
+
+/* This test case is extracted from Perl version 5.7.3.  It is
+   in the Perl_unpack_str function of the pp_pack.c source file.
+
+   GCC 2.95.2 improperly assumes that it can compensate for an
+   extra fsub by performing a fadd.  This would work in
+   fixed-point arithmetic, but does not work in floating-point
+   arithmetic.
+
+   This problem has been seen on HP-UX and on Stratus VOS, both
+   of which have an HP PA-RISC target (hppa1.1).  The Stratus
+   bug number is gnu_g++-220.  */
+
+/* #define _POSIX_C_SOURCE 199506L -- added by Configure */
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+
+void test(double *result)
+{
+	float	afloat;
+	double	adouble;
+	int		checksum = 0;
+	unsigned	cuv = 0;
+	double	cdouble = 0.0;
+	const int	bits_in_uv = 8 * sizeof(cuv);
+
+	checksum = 53;
+	cdouble = -1.0;
+
+	if (checksum) {
+		if (checksum > bits_in_uv) {
+			double trouble;
+
+			adouble = (double) (1 << (checksum & 15));
+
+			while (checksum >= 16) {
+				checksum -= 16;
+				adouble *= 65536.0;
+			}
+
+			/* At -O1, GCC 2.95.2 compiles the following loop
+			   into:
+
+			   L$0014
+				fcmp,dbl,>= %fr4,%fr0
+				ftest
+				b L$0014
+				fadd,dbl %fr4,%fr12,%fr4
+				fsub,dbl %fr4,%fr12,%fr4
+
+				This code depends on the floading-add and
+				floating-subtract retaining all of the
+				precision present in the operands.  There is
+				no such guarantee when using floating-point,
+				as this test case demonstrates.
+
+				The code is okay at -O0.  */
+
+			while (cdouble < 0.0)
+				cdouble += adouble;
+
+			cdouble = modf (cdouble / adouble, &trouble) * adouble;
+		}
+	}
+
+	*result = cdouble;
+}
+
+int main (int argc, char ** argv)
+{
+double	value;
+
+	test (&value);
+
+	if (argc == 2 && !strcmp(argv[1],"-v"))
+		printf ("value = %.18e\n", value);
+
+	if (value != 9.007199254740991e+15) {
+		printf ("t001 fails!\n");
+		return -1;
+	}
+	else {
+		printf ("t001 works.\n");
+		return 0;
+	}
+}