Shift 1 and multiply vs direct shift-CodePudding

I came across code similar to this in the ARM CMSIS-NN library:

int32_t val, shift;

// code that initializes val and shift

int32_t result = val * (1 << shift);

which aims to multiply val by some power of two value x, with shift being the exponent, i.e. x=pow(2,shift). Why are they not simply shifting? Like so

int32_t result = val << shift;

Is there something special that I am missing? Can the compiler optimize the former operation in some special way?

EDIT: What confuses me is that they are using "simple shifts" throughout the code. Additionally, the code should be highly optimized. But I guess modern compilers will figure out by themselves, that shifting is the way to go (instead of multiplying)?

CodePudding user response：

It is always sign correct and forces the use of the proper FPU instructions and works with any type of data.