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Improve performance of PowerPC64 ZEND_SIGNED_MULTIPLY_LONG

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Detecting overflow with the XER is slow, partially because we have to
clear it before use. We can do better by using a trick where we compare
the high 64 bits of the result with the low 64 bits shifted right
63 bits.

This is 7% faster on a POWER8 running a simple testcase:

<?php
        function testcase($count = 100000000) {
                for ($i = 0; $i < $count; $i++) {
                        $x = 1;
                        $x = $x * 2;
                        $x = $x * 2;
                        $x = $x * 2;
                        $x = $x * 2;
                }
        }

        testcase();
?>
This commit is contained in:
Anton Blanchard 2015-05-26 22:42:13 +10:00 committed by Remi Collet
parent a581910a76
commit 305199a131
1 changed files with 13 additions and 14 deletions
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25
Zend/zend_multiply.h
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@ -75,19 +75,18 @@
#elif defined(__powerpc64__) && defined(__GNUC__)
#define ZEND_SIGNED_MULTIPLY_LONG(a, b, lval, dval, usedval) do { \
long __tmpvar; \
__asm__("li 14, 0\n\t" \
"mtxer 14\n\t" \
"mulldo. %0, %2,%3\n\t" \
"xor %1, %1, %1\n\t" \
"bns+ 0f\n\t" \
"li %1, 1\n\t" \
"0:\n" \
: "=r"(__tmpvar),"=r"(usedval) \
: "r"(a), "r"(b) \
: "r14", "cc"); \
if (usedval) (dval) = (double) (a) * (double) (b); \
else (lval) = __tmpvar; \
long __low, __high; \
__asm__("mulld %0,%2,%3\n\t" \
"mulhd %1,%2,%3\n" \
: "=&r"(__low), "=&r"(__high) \
: "r"(a), "r"(b)); \
if ((__low >> 63) != __high) { \
(dval) = (double) (a) * (double) (b); \
(usedval) = 1; \
} else { \
(lval) = __low; \
(usedval) = 0; \
} \
} while (0)
#elif SIZEOF_ZEND_LONG == 4