fix: fix the possible overflow case in the current implementation

[xieyuschen]

Possible Overflow

Currently, the Add API of Counter and the similar implementation has the overflow problem. I write a test case to demonstrate it by the test case TestCounterAddExcess in the commit 3227fc0. And the output verifies the overflow does happen as expected.

➜  client_golang git:(3227fc0) go version
go version go1.21.3 darwin/arm64
➜  client_golang git:(3227fc0) go test ./prometheus
--- FAIL: TestCounterAddExcess (0.00s)
    counter_test.go:46: oops! overflow
    counter_test.go:63: failed because the internal overflow
    counter_test.go:69: verify the overflow case

Proposal

I think it's nice to fix it as it's a possible case. I haven't checked much about the history discussions about this topic. As a result, I would like to discuss with the maintainers to see whether you would like to accept such changes or not.

We need to check two additional cases for the possible overflows:

• the input float v is large enough so it will lose precise during casting by uint.
• the addition overflows

One step further, we can add the valInt value into the float set valBits and then reset the valInt to zero.

Regards.

[xieyuschen]

i just found that the casting works different in in linux and macos. will check further tomorrow, so close it.