In general the idea LGTM. It it is slightly dangerous if dict structure is broken. j is incremented only when value != NULL, and if ma_used is not correct, this can cause reading out of the end of an array. Of course this should never happen. But if there is a chance to add some assertions or additional checks in debug mode, it would be nice. Unless this complicate the code to much.

The i counter is not used in some loops. It can be eliminated.