Using go version 1.10.3 sometimes a problem involving sweep built in go function ocoured. Substituting make([]C.float, dataInLength) to C.malloc(C.sizeof_float * C.ulong(dataInLength)) this problem didn't ocour anymore because of the use of C memory allocation.

Instead of truncating the ratio, round it upwards to make sure we always allocate enough samples. This gets rid of the "margin" (which wasn't large enough for all cases, anyway), and supports ratios less than 1, which previously only returned up to 20 samples.

The Simple function creates a C pointer to Go object, which becomes a dangling pointer if the Go gc frees the Go object while the cgo function is running.

There are two open pull requests both dealing with this issue (I just noticed there is an existing pull request for the same issue).

In func Simple, the inputBuffer and outputBuffer are created as slices, then the address of each is copied to a C pointer (member of struct allocated with malloc). At this point, the Go gc can free or move the memory - go only guarantees that the gc won't free an object if the address of the object is passed as a cgo function parameter, no such guarantee is made for pointers in structs allocated with malloc.

Fix this by passing inputBuffer and outputBuffer as parameters to the cgo call.

Fixes: runtime: pointer 0xc000c32000 to unused region of span span.base()=0xc00062e000 span.limit=0xc00062fe00 span.state=1 fatal error: found bad pointer in Go heap (incorrect use of unsafe or cgo?)