>So what about sending the data to memory, as they're doing, then bring it to a VFP array using your library, make the modifications in the array with VFP, and then sending the array back in just one time ?
>That would avoid all those SYS(2600) calls...

MMMMhhh, vfp arrays are not really speed kings as well...
Depending on the hardware and string length I think you will see substr() perform faster on small strings (around 512 bytes) and sys(2600) in read mode be faster for larger strings. Just accessing single char vfp array elements will be slower (although the different CPU's types can show markedly different relative execution times in that area).

regards

thomas