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Hi, the following code for STM32F4 (Cortex-M4):
float fZero= 0.; float fInfinity; short sTestPlus, sTestNeg; int main( void){ fInfinity= 1.f/fZero; sTestPlus= fInfinity; fInfinity= -1.f/fZero; sTestNeg= fInfinity; while(1); }
should result in the values sTestPlus= 0x7FFF and sTestNeg= 0x8000. Instead it produces 0xFFFF and 0x0000.
The reason is, that the compiler uses the signed 32bit convert (leading to the correct result 0x7FFFFFFF and 0x80000000), and then just cuts out the lower short, which is really poor.
As I understand, it is no problem with Cortex M4 to do float to signed16 using the VCVT command in a more sophisticated way (specifying 16bit).
Is there a way to get this done?
But conversion from int to float is nothing mystical - why should this be not documented?
Well, I don't know. Why don't you ask Keil? It's their documentation, after all. Or maybe I didn't dig deep enough.
At least - if I should be able to use Cortex M4 efficiently, it would be necessary that there is some inline/intrinsic possibility to use this VCVT command with its full power.
Definitely. Sounds like a feature request that should be directed to Keil.