Fix several issues with includes and redundant comparisons.

include/sprs.h

@@ -1,6 +1,7 @@
 #ifndef LIBDS_SPRS_HEADER
 #define LIBDS_SPRS_HEADER
 
+#include <stddef.h>
 #include "libds.h"
 
 /**

include/vec.h

@@ -3,6 +3,7 @@
 
 #define LIBDS_VEC_CAPACITY 4
 
+#include <stddef.h>
 #include "libds.h"
 
 /**

src/sprs.c

@@ -38,7 +38,7 @@ void sprs_put(sprs* sprs, int index, void* data){
   }
 }
 int sprs_contains(sprs* sprs, int index){
-  return index >= 0 && sprs->sparse[index].index >= 0 && sprs->sparse[index].index < sprs->size && sprs->dense[sprs->sparse[index].index] == index;
+  return index >= 0 && sprs->sparse[index].index < sprs->size && sprs->dense[sprs->sparse[index].index] == index;
 }
 void* sprs_get(sprs* sprs, int index){
   void* data = NULL;

src/vec.c

@@ -92,7 +92,7 @@ int vec_foreach(vec* v, void* data, compare_func compare, foreach_func foreach,
 
 void* vec_index(vec* v, size_t index) {
   void* to_return = NULL;
-  if (index < v->capacity && index >= 0) {
+  if (index < v->capacity) {
     to_return = ((void**) v->data)[index];
   }
   return to_return;