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arithmetic overflow check improved:

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- Now it should be more unlikely to prevent arithmetic overflows. Please test.
- This change costs about 20 bytes flash
- Unfortunately still not bullet proof. A bullet proof check would cost additionally 100bytes flash, is it worth?
- To get in dangerous areas, both weight and offset needs to be set very high. Without offset no more overruns should occur.
This commit is contained in:
open.20.fsguruh@xoxy.net
2013-02-28 05:37:16 +00:00
parent 792412f5fe
commit 82783013fd
1 changed files with 10 additions and 4 deletions
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src/open9x.cpp
+10 -4
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@@ -758,6 +758,9 @@ int16_t applyLimits(uint8_t channel, int32_t value)
// unfortunately the constants and 32bit compares generates about 50 bytes codes; didn't find a way to get it down.
// But I think it is worth
value = limit(int32_t(-RESXl*256),value,int32_t(RESXl*256)); // saves 2 bytes compared to solution below
// try also limit 0xFFFFF
// value = limit(int32_t(-0xFFFFF),value,int32_t(0xFFFFF)); // saves 2 bytes compared to solution below
// if (value>RESXl*256) value = RESXl*256; // no bigger values allowed, prevent early overruns
// if (value<-RESXl*256) value = -RESXl*256; // no smaller values allowed, prevent early overruns
#endif
@@ -2823,20 +2826,22 @@ void perOut(uint8_t mode, uint8_t tick10ms)
} words_t;
int32_t dword;
});
u_int16int32_t tmp;
tmp.dword=*ptr;
if (tmp.dword<0) {
tmp.words_t.hi|=0xFF80;
if ((tmp.words_t.hi&0xFF80)!=0xFF80) tmp.words_t.hi=0xFF86; // set to min nearly
//tmp.bytes_t.h4=0xFF;
//tmp.bytes_t.h3|=0x80;
} else {
if ((tmp.words_t.hi|0x007F)!=0x007F) tmp.words_t.hi=0x00079; // set to max nearly
// tmp.bytes_t.h4=0x00;
// tmp.bytes_t.h3&=0x7F;
tmp.words_t.hi&=0x007F;
// tmp.words_t.hi&=0x007F;
}
*ptr=tmp.dword;
// this implementation saves 32bytes flash
// this implementation saves 18bytes flash
/* dv=*ptr>>8;
if (dv>(32767-RESXl)) {
@@ -2844,7 +2849,8 @@ void perOut(uint8_t mode, uint8_t tick10ms)
} else if (dv<(-32767+RESXl)) {
*ptr=(-32767+RESXl)<<8;
}*/
//*ptr=limit( int32_t((-32767+RESXl)<<8), dv, int32_t((32767-RESXl)<<8)); // limit code cost 80 bytes
// *ptr=limit( int32_t(int32_t(-1)<<23), *ptr, int32_t(int32_t(1)<<23)); // limit code cost 72 bytes
// *ptr=limit( int32_t((-32767+RESXl)<<8), *ptr, int32_t((32767-RESXl)<<8)); // limit code cost 80 bytes
#endif
} //endfor mixers