iOS5 Xcode4.2 floating-point byte align error?

Question

Look at this code:

this is struct definition file with 1byte struct packing (for socket networking)

#pragma pack(1)

typedef struct _TestStruct1 {

doubl         


        

Answer 1

I had a problem like this, involving floating-point miscalculations but in UI positioning code. I fixed it by adding:

-mno-thumb

to the "Other C Flags" options under Build Settings, for armv6 devices only ("Add Build Setting" > "Add Conditional Setting").

I don't pretend to understand exactly what's happening here, but by adding this build setting you're disabling the Thumb instruction set, which according to some (http://wanderingcoder.net/2010/07/19/ought-arm/) is not recommended for armv6 builds anyway. Thumb changes the way floating-point calculations work.