Compiler/CCSTUDIO-MSP: How to specify floating point constants in hex?

Jeffrey Lomibao76

Part Number: CCSTUDIO-MSP
Other Parts Discussed in Thread: MSP430F5438A

Tool/software: TI C/C++ Compiler

I'm trying to specify a single-precision floating point NaN default in flash, eg. const float value = 0x7FA00000. The compiler is treating the hex value as an integer and converting it to a floating huge floating point value. How do I tell the compiler to use the hex value as is?

over 8 years ago

0 George Mock over 8 years ago

TI__Guru**** 252560 points

Which CPU family do you use?

-George

0 Jeffrey Lomibao76 over 8 years ago in reply to George Mock

Expert 1210 points

MSP430, specifically MSP430F5438A.

0 George Mock over 8 years ago in reply to Jeffrey Lomibao76

TI__Guru**** 252560 points

Use the compiler intrinsics detailed in this forum post.

Thanks and regards,

-George

0 Jeffrey Lomibao76 over 8 years ago in reply to George Mock

Expert 1210 points

I tried both
const float value = __u32_bits_as_f32(0x7FA00000);
and
float value = __u32_bits_as_f32(0x7FA00000);

But the compiler is giving me this error: #60 function call is not allowed in a constant expression.
Is there another way available?

0 Archaeologist over 8 years ago in reply to Jeffrey Lomibao76

TI__Guru* 84285 points

Which version of the TI MSP430 compiler do you use? (This is not the same as the CCS version).
If it is a version which supports C99, you can use C99 hex float constants (q.v.)
If it does not support C99, it needs to be somewhat recent to support the intrinsic __u32_bits_as_f32.

0 Jeffrey Lomibao76 over 8 years ago in reply to Archaeologist

Expert 1210 points

I am using ti-cgt-msp430_16.9.6.LTS.
Could you please provide an example of how to define a NaN value using C99 hex float notation. I am not familiar with this.

0 Archaeologist over 8 years ago in reply to Jeffrey Lomibao76

TI__Guru* 84285 points

Oh, you don't, if you have C99 mode enabled, you just use the "NAN" macro:
\#include <math.h>
float nan = NAN;
float inf = INFINITY;
float pi = 0x1.921fb6p+1;

0 Jeffrey Lomibao76 over 8 years ago in reply to Archaeologist

Expert 1210 points

How do I enable C99 mode?

Code Composer Studio™︎

Code Composer Studio forum

Compiler/CCSTUDIO-MSP: How to specify floating point constants in hex?