pointers - C array = array faster than memcpy() -

i have piece of c code trying optimise involves setting array b. using memcpy achieve this, , works, it's not fast enough. i.e.

double a[4] = {1.0, 2.0, 3.0, 4.0}; double b[4]; memcpy(b, a, sizeof(a)); 

this basic example, program similar uses 9000 doubles. know use of pointers can save lot of time, i'm not sure how it. you're appreciated.

edit: don't need keep array, can discarded. need transfer b.

i use values in b determine new values a. goes through while loop checking convergence in data.

in case may able avoid copying, if switch arrays , forth, (which backwards wrote; adjust needed):

double array1[size], array2[size]; double* = array1, double* b = array2; generate_initial_values(array1);  (;;) {     // either      memcpy(b, a, sizeof array1); // sizeof either array do; *don't* use sizeof or b, size of pointer, not of array     update_values_in_b(b);      // or, better:     produce_modified_values_in_b_from_a(a, b);      if (converged(a, b)) break;     // switch arrays     double* temp_ptr = a;     = b;     b = temp_ptr; } 

doing second way faster if works you. if must memcpy, can try stuff in very fast memcpy image processing?, best use memcpy , set compiler's optimization level high possible. sure #include <string.h> , size argument memcpy compile-time constant (it above), , @ generated assembly code verify compiler inlining copy.

edit: wait, here's thought, doesn't require switching arrays:

double a[size], b[size]; generate_initial_values(a);  (;;) {     produce_modified_values_in_second_array_from_first(a, b);     if (converged(a, b)) break;     produce_modified_values_in_second_array_from_first(b, a);     if (converged(b, a)) break; } 

when exit loop don't know array has latest values, if they've converged don't care. if do, can set pointer latest values, or use function:

void calling_function(void) {     ...     double a[size], b[size];     generate_initial_values(a);     double* great_values = get_great_values(a, b); // returns either or b     ... }  double* get_great_values(double* a1, double* a2) {     (;;)     {         produce_modified_values_in_second_array_from_first(a1, a2);         if (converged(a1, a2)) return a2;         produce_modified_values_in_second_array_from_first(a2, a1);         if (converged(a2, a1)) return a1;     } }