In perl.git, the branch blead has been updated
<http://perl5.git.perl.org/perl.git/commitdiff/60d5033292df238895c866316ce2f72eb76e3bb9?hp=f2e32b2c677945ce6a36531a7cd5696dc1ca2cef>
- Log -----------------------------------------------------------------
commit 60d5033292df238895c866316ce2f72eb76e3bb9
Author: Jarkko Hietaniemi <j...@iki.fi>
Date: Sun Jul 17 10:53:27 2016 +0300
VAX: perl.h: document the VAX fp better/more
M perl.h
commit 234b86dfbf86ead1bb11552473feb1a73b654443
Author: Jarkko Hietaniemi <j...@iki.fi>
Date: Sun Jul 17 10:48:12 2016 +0300
VAX: Configure: the VAX fp not really little-endian
M Configure
-----------------------------------------------------------------------
Summary of changes:
Configure | 12 ++++++------
perl.h | 37 ++++++++++++++++++++++++++++++++-----
2 files changed, 38 insertions(+), 11 deletions(-)
diff --git a/Configure b/Configure
index 944bf66..3a96351 100755
--- a/Configure
+++ b/Configure
@@ -10145,7 +10145,7 @@ int main() {
exit(0);
}
if (b[0] == 0xCC && b[3] == 0xCC) {
- /* VAX format F */
+ /* VAX format F, 32-bit PDP-style mixed endian. */
printf("9\n");
exit(0);
}
@@ -10176,12 +10176,12 @@ int main() {
exit(0);
}
if (b[0] == 0xCC && b[7] == 0xCC) {
- /* VAX format D, 64-bit little-endian. */
+ /* VAX format D, 64-bit PDP-style mixed endian. */
printf("10\n");
exit(0);
}
if (b[0] == 0xD9 && b[7] == 0x99) {
- /* VAX format G, 64-bit little-endian. */
+ /* VAX format G, 64-bit PDP-style mixed endian. */
printf("11\n");
exit(0);
}
@@ -10219,9 +10219,9 @@ case "$doublekind" in
6) echo "You have IEEE 754 128-bit big endian doubles." >&4 ;;
7) echo "You have IEEE 754 64-bit mixed endian doubles (32-bit LEs in BE)."
>&4 ;;
8) echo "You have IEEE 754 64-bit mixed endian doubles (32-bit BEs in LE)."
>&4 ;;
-9) echo "You have VAX format F 32-bit little-endian doubles." >&4 ;;
-10) echo "You have VAX format D 64-bit little-endian doubles." >&4 ;;
-11) echo "You have VAX format G 64-bit little-endian doubles." >&4 ;;
+9) echo "You have VAX format F 32-bit PDP-style mixed endian doubles." >&4 ;;
+10) echo "You have VAX format D 64-bit PDP-style mixed endian doubles." >&4 ;;
+11) echo "You have VAX format G 64-bit PDP-style mixed endian doubles." >&4 ;;
*) echo "Cannot figure out your double. You CRAY, or something?" >&4 ;;
esac
$rm_try
diff --git a/perl.h b/perl.h
index 2702cc1..c6c18db 100644
--- a/perl.h
+++ b/perl.h
@@ -6771,11 +6771,38 @@ extern void moncontrol(int);
# define DOUBLE_MIX_ENDIAN
#endif
-/* Even though the VAX formats are kind of little-endian,
- * they are not really fully little-endian like Intel IEEE,
- * but neither are they really IEEE-mixed endian like the
- * mixed-endian ARM IEEE formats (with swapped bytes).
- * The VAX format ultimately come from PDP. */
+/* The VAX fp formats are neither consistently little-endian nor
+ * big-endian, and neither are they really IEEE-mixed endian like
+ * the mixed-endian ARM IEEE formats (with swapped bytes).
+ * Ultimately, the VAX format ultimately came from the PDP.
+ *
+ * The ordering of the parts in VAX floats is quite vexing.
+ * In the below the fraction_n are the mantissa bits.
+ * The fraction_1 is the most significant (numbering as by DEC/Digital),
+ * and the rightmost bit in each fraction is the least significant.
+ * This means for example that both the the most and least significant
+ * bits are in the middle of the floats, not at either end.
+ *
+ * F fraction_2:16 sign:1 exp:7 fraction_1:7
+ * (exponent bias 128)
+ *
+ * D fraction_2:16 sign:1 exp:7 fraction_1:7
+ * fraction_4:16 fraction_3:16
+ * (exponent bias 128)
+ *
+ * G fraction_2:16 sign:1 exp:11 fraction_1:7
+ * fraction_4:16 fraction_3:16
+ * (exponent bias 1024)
+ *
+ * H fraction_1:16 sign:1 exp:15
+ * fraction_3:16 fraction_2:16
+ * fraction_5:16 fraction_4:16
+ * fraction_7:16 fraction_6:16
+ * (exponent bias 16384)
+ *
+ * The formats T and X are available on the Alpha (and IA64?)
+ * and are equivalent with the IEEE 754 64 and 128 bit formats.
+ */
#ifdef DOUBLE_IS_VAX_FLOAT
# define DOUBLE_VAX_ENDIAN
--
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