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Fix calculation of 2**30

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In exponent(), 'base *= base;' should not run
when base is 65536, since it overflows an int32_t.

This also optimizes exponent() based on
gcc and clang -O3 test cases in godbolt.org.
This commit is contained in:
Rangi
2021-02-17 09:25:02 -05:00
parent d049ffc0f0
commit 748e7dd4c7
3 changed files with 11 additions and 5 deletions
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6
src/asm/rpn.c
View File

@@ -283,14 +283,16 @@ static int32_t shift(int32_t shiftee, int32_t amount)
} }
} }
static int32_t exponent(int32_t base, int32_t power) static int32_t exponent(int32_t base, uint32_t power)
{ {
int32_t result = 1; int32_t result = 1;
while (power) { for (;;) {
if (power % 2) if (power % 2)
result *= base; result *= base;
power /= 2; power /= 2;
if (!power)
break;
base *= base; base *= base;
} }

6
src/link/patch.c
View File

@@ -21,14 +21,16 @@
#include "extern/err.h" #include "extern/err.h"
static int32_t exponent(int32_t base, int32_t power) static int32_t exponent(int32_t base, uint32_t power)
{ {
int32_t result = 1; int32_t result = 1;
while (power) { for (;;) {
if (power % 2) if (power % 2)
result *= base; result *= base;
power /= 2; power /= 2;
if (!power)
break;
base *= base; base *= base;
} }

4
test/asm/math.asm
View File

@@ -12,7 +12,9 @@ v equs "Y +"
ENDM ENDM
test (v 2)*(v 10)**(v 2)*(v 2) == (v 400) test (v 2)*(v 10)**(v 2)*(v 2) == (v 400)
test -(v 3)**(v 4) == v -81 test -(v 3)**(v 4) == (v -81)
test (v 1) << (v 30) == (v $4000_0000)
test (v 2)**(v 30) == (v $4000_0000)
assert DIV(5.0, 2.0) == 2.5 assert DIV(5.0, 2.0) == 2.5
assert DIV(-5.0, 2.0) == -2.5 assert DIV(-5.0, 2.0) == -2.5