Unsigned Modulo
Unsigned Modulo
- Subject: Unsigned Modulo
- From: "Gerriet M. Denkmann" <email@hidden>
- Date: Wed, 12 Aug 2015 17:12:46 +0700
OS X 10.10.4, Xcode 7 beta 3
This code produces some (for me) unexpected results:
NSUInteger unsignedSize = 3;
NSInteger signedSize = 3;
for ( NSInteger rawValue = -6; rawValue < 5; rawValue++ )
{
NSInteger modValueU = rawValue;
NSInteger modValueS = rawValue;
modValueU %= unsignedSize;
modValueS %= signedSize;
fprintf(stderr,"rawValue %+2ld modValueU %+2ld modValueS %+2ld\n", rawValue, modValueU, modValueS);
};
rawValue -6 modValueU +1 modValueS +0 expected modValueU = 0
rawValue -5 modValueU +2 modValueS -2 expected modValueU = 1
rawValue -4 modValueU +0 modValueS -1 expected modValueU = 2
rawValue -3 modValueU +1 modValueS +0 expected modValueU = 0
rawValue -2 modValueU +2 modValueS -2 expected modValueU = 1
rawValue -1 modValueU +0 modValueS -1 expected modValueU = 2
rawValue +0 modValueU +0 modValueS +0
rawValue +1 modValueU +1 modValueS +1
rawValue +2 modValueU +2 modValueS +2
rawValue +3 modValueU +0 modValueS +0
rawValue +4 modValueU +1 modValueS +1
Probably the answer is: works as documented (but I can’t figure out the rule it is following).
But even if so: why are there no warnings, compiling with these flags:
CLANG_WARN_IMPLICIT_SIGN_CONVERSION
GCC_WARN_ABOUT_POINTER_SIGNEDNESS
GCC_WARN_SIGN_COMPARE
Gerriet.
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