High cost of failed Math.*Exact calls

[Raffaello Giulietti]

On 2024-12-12 23:58, Charles Oliver Nutter wrote:
> 
> Question two: Am I losing the benefits of *Exact if I use the following 
> code to "pre-check" for overflow?
> 
> long high = Math.multiplyHigh(a, b);
> if (high == 0) return Math.multiplyExact(a, b);
> return bigIntegerMultiply(a, b);
> 

For your specific multiplication use case you might try with

long high = Math.multiplyHigh(a, b);
long low = a * b;
if (high == 0) return low;
return "the big integer consisting of high and low";

It might be possible that the multiplyHigh() and * on the same operands, 
when appearing adjacent to each other, get optimized to just one 
instruction.
And if not, they might be executed "in parallel" inside the CPU.


HTH
Raffaello