Is this a suitable patch to apply to Configure (and backport to the metaconfig
units), for the purpose of testing whether 0.0 is stored as all bits zero in
memory? It's a useful thing to know, because if it's true (which I think is
generally the case), then memset of a block of memory to 0 is sufficient to
correctly initialise any NVs that it contains. It's quite safe for it to
default to #undef on non-Configure platforms.
In theory we should also be checking that NULL pointers are stored as all bits
zero, but I think that that portability battle is already lost - we already
Zero() SV bodies that contain pointers and expect things to work.
Also, I think that by adding another symbol to config_h.SH this breaks VMS,
but I can't remember the correct fix, or where it goes. Can someone help?
Nicholas Clark
--- Configure.orig Tue May 31 07:09:02 2005
+++ Configure Sat Jun 18 17:55:48 2005
@@ -1002,6 +1002,7 @@ perl5=''
perladmin=''
perlpath=''
d_nv_preserves_uv=''
+d_nv_zero_is_allbits_zero=''
i16size=''
i16type=''
i32size=''
@@ -14833,6 +14834,128 @@ esac
$rm -f try.* try
+$echo "Checking whether NV 0.0 is all bits zero in memory..." >&4
+: volatile so that the compiler has to store it out to memory.
+if test X"$d_volatile" = X"$define"; then
+ volatile=volatile
+fi
+$cat <<EOP >try.c
+#include <stdio.h>
+#$i_stdlib I_STDLIB
+#ifdef I_STDLIB
+#include <stdlib.h>
+#endif
+#$i_string I_STRING
+#ifdef I_STRING
+# include <string.h>
+#else
+# include <strings.h>
+#endif
+#include <sys/types.h>
+#include <signal.h>
+#ifdef SIGFPE
+$volatile int bletched = 0;
+$signal_t blech(s) int s; { bletched = 1; }
+#endif
+
+int checkit($nvtype d, char *where) {
+ unsigned char *p = (char *)&d;
+ unsigned char *end = p + sizeof(d);
+ int fail = 0;
+
+ while (p < end)
+ fail += *p++;
+
+ if (!fail)
+ return 0;
+
+ p = (char *)&d;
+ printf("No - %s: 0x", where);
+ while (p < end)
+ printf ("%02X", *p++);
+ printf("\n");
+ return 1;
+}
+
+int main(int argc, char **argv) {
+ $nvtype d = 0.0;
+ int fail = 0;
+ fail += checkit(d, "0.0");
+
+ /* The compiler shouldn't be assuming that bletched is 0 */
+ d = bletched;
+
+ fail += checkit(d, "bleched");
+
+#ifdef SIGFPE
+ signal(SIGFPE, blech);
+#endif
+
+ /* Paranoia - the compiler should have no way of knowing that ANSI says
+ that argv[argc] will always be NULL. Actually, if it did assume this it
+ would be buggy, as this is C and main() can be called from elsewhere in
+ the program. */
+ d = argv[argc] ? 1 : 0;
+
+ if (d) {
+ printf("Odd argv[argc]=%p, d=%g\n", argv[argc], d);
+ }
+
+ fail += checkit(d, "ternary");
+
+ memset(&d, sizeof(d), argv[argc] ? 1 : 0);
+
+ if (d != 0.0) {
+ printf("No - memset doesn't give 0.0\n");
+ /* This might just blow up: */
+ printf("(gives %g)\n", d);
+ return 1;
+ }
+
+#ifdef SIGFPE
+ if (bletched) {
+ printf("No - something bleched\n");
+ return 1;
+ }
+#endif
+ if (fail) {
+ printf("No - %d fail(s)\n", fail);
+ return 1;
+ }
+ printf("Yes\n");
+ return 0;
+}
+EOP
+set try
+
+d_nv_zero_is_allbits_zero="$undef"
+if eval $compile; then
+ xxx="`$run ./try`"
+ case "$?" in
+ 0)
+ case "$xxx" in
+ Yes) cat >&4 <<EOM
+0.0 is represented as all bits zero in memory
+EOM
+ d_nv_zero_is_allbits_zero="$define"
+ ;;
+ *) cat >&4 <<EOM
+0.0 is not represented as all bits zero in memory
+EOM
+ d_nv_zero_is_allbits_zero="$undef"
+ ;;
+ esac
+ ;;
+ *) cat >&4 <<EOM
+0.0 is not represented as all bits zero in memory
+EOM
+ d_nv_zero_is_allbits_zero="$undef"
+ ;;
+ esac
+fi
+
+$rm -f try.* try
+
: check for off64_t
echo " "
@@ -21012,6 +21135,7 @@ d_mymalloc='$d_mymalloc'
d_nice='$d_nice'
d_nl_langinfo='$d_nl_langinfo'
d_nv_preserves_uv='$d_nv_preserves_uv'
+d_nv_zero_is_allbits_zero='$d_nv_zero_is_allbits_zero'
d_off64_t='$d_off64_t'
d_old_pthread_create_joinable='$d_old_pthread_create_joinable'
d_oldpthreads='$d_oldpthreads'
--- config_h.SH.orig Thu May 26 12:56:06 2005
+++ config_h.SH Sat Jun 18 17:31:21 2005
@@ -3235,6 +3235,10 @@ sed <<!GROK!THIS! >$CONFIG_H -e 's!^#und
* This symbol contains the number of bits a variable of type NVTYPE
* can preserve of a variable of type UVTYPE.
*/
+/* NV_ZERO_IS_ALLBITS_ZERO
+ * This symbol, if defined, indicates that a variable of type NVTYPE
+ * stores 0.0 in memory as all bits zero.
+ */
#define IVTYPE $ivtype /**/
#define UVTYPE $uvtype /**/
#define I8TYPE $i8type /**/
@@ -3263,6 +3267,7 @@ sed <<!GROK!THIS! >$CONFIG_H -e 's!^#und
#define NVSIZE $nvsize /**/
#$d_nv_preserves_uv NV_PRESERVES_UV
#define NV_PRESERVES_UV_BITS $nv_preserves_uv_bits
+#$d_nv_zero_is_allbits_zero NV_ZERO_IS_ALLBITS_ZERO
#if UVSIZE == 8
# ifdef BYTEORDER
# if BYTEORDER == 0x1234
--- Porting/Glossary.orig Fri May 20 09:23:14 2005
+++ Porting/Glossary Sat Jun 18 17:32:22 2005
@@ -1383,6 +1383,10 @@ d_nv_preserves_uv (perlxv.U):
This variable indicates whether a variable of type nvtype
can preserve all the bits a variable of type uvtype.
+d_nv_zero_is_allbits_zero (perlxv.U):
+ This variable indicates whether a variable of type nvtype
+ stores 0.0 in memory as all bits zero.
+
d_off64_t (d_off64_t.U):
This symbol will be defined if the C compiler supports off64_t.
