Expression engine: fixes for evaluation optimization.

Author: malloch

src/expression.c

@@ -262,7 +262,7 @@ void mpr_expr_set_var_updated(mpr_expr expr, int var_idx)
                   && var_idx != expr->mute_ctl);
     expr->vars[var_idx].flags |= VAR_SET_EXTERN;
     /* Reset expression offset to 0 in case other variables are initialised from this one. */
-    expr->stack->init_offset = 0;
+    expr->stack->initialized = 0;
     return;
 }
 

src/expression/expr_evaluator.h

@@ -117,8 +117,19 @@ int mpr_expr_eval(mpr_expr expr, ebuffer buff, mpr_value *v_in, mpr_value *v_var
     uint8_t *lens = buff->lens;
     mpr_type *types = buff->types;
 
-    if (v_out && mpr_value_get_num_samps(v_out, inst_idx) > 0) {
-        tok += stk->init_offset;
+    if (v_out) {
+        if (stk->initialized) {
+#if TRACE_EVAL
+            printf("advancing start token to %d\n", stk->init_offset);
+#endif
+            tok += stk->init_offset;
+        }
+        else {
+#if TRACE_EVAL
+            printf("initializing from token 0\n");
+#endif
+            stk->initialized = 1;
+        }
     }
 
     if (v_vars) {

src/expression/expr_stack.h

@@ -13,6 +13,7 @@ typedef struct _estack
     uint8_t num_tokens;
     uint8_t size;
     uint8_t vec_len;
+    uint8_t initialized;
 } estack_t, *estack;
 
 #if TRACE_PARSE
@@ -34,6 +35,7 @@ void estack_cpy(estack to, estack from)
     to->num_tokens = from->num_tokens;
     to->vec_len = from->vec_len;
     to->init_offset = from->init_offset;
+    to->initialized = from->initialized;
     to->tokens = malloc(sizeof(etoken_t) * (size_t)from->num_tokens);
     memcpy(to->tokens, from->tokens, sizeof(etoken_t) * (size_t)from->num_tokens);
 
@@ -259,6 +261,7 @@ static int precompute(estack stk, uint8_t num_tokens_to_compute)
 
     /* temporarily set the stk 'offset' variable */
     stk->init_offset = stk->num_tokens - num_tokens_to_compute;
+    stk->initialized = 1;
     stk->vec_len = vec_len;
     expr = mpr_expr_new(0, 0, stk);
     buff = mpr_expr_new_eval_buffer(expr);
@@ -310,13 +313,13 @@ static int precompute(estack stk, uint8_t num_tokens_to_compute)
     tok->gen.datatype = type;
     tok->gen.vec_len = vec_len;
     stk->num_tokens = stk->init_offset + 1;
-    stk->init_offset = 0;
 
 done:
     mpr_value_free(val);
     mpr_expr_free(expr);
     mpr_expr_free_eval_buffer(buff);
     stk->init_offset = 0;
+    stk->initialized = 0;
     return ret;
 }