regcomp.c: Change variable meaning and hence name

I think it is clearer to note that what happens here is that the node
can match fewer characters than what it would normally be thought to,
and hence the returned value should be subtracted; it also means that
the absolute value need not be taken

3 files changed, 37 insertions, 33 deletions

diff --git a/embed.fnc b/embed.fnc
index 5e93cabb11..d6980d609c 100644
--- a/embed.fnc
+++ b/embed.fnc
@@ -1899,7 +1899,7 @@ Es	|void	|regtail	|NN struct RExC_state_t *pRExC_state \
 Es	|SV *	|reg_scan_name	|NN struct RExC_state_t *pRExC_state \
 				|U32 flags
 Es	|U32	|join_exact	|NN struct RExC_state_t *pRExC_state \
-				|NN regnode *scan|NN IV *min_change  \
+				|NN regnode *scan|NN UV *min_subtract  \
 				|NN bool *has_exactf_sharp_s  \
 				|U32 flags|NULLOK regnode *val|U32 depth
 EsRn	|char *	|regwhite	|NN struct RExC_state_t *pRExC_state \
diff --git a/proto.h b/proto.h
index 0c7a321489..fcf5ab9a28 100644
--- a/proto.h
+++ b/proto.h
@@ -6371,13 +6371,13 @@ PERL_STATIC_INLINE void	S_invlist_trim(pTHX_ SV* const invlist)
 #define PERL_ARGS_ASSERT_INVLIST_TRIM	\
 	assert(invlist)
 
-STATIC U32	S_join_exact(pTHX_ struct RExC_state_t *pRExC_state, regnode *scan, IV *min_change, bool *has_exactf_sharp_s, U32 flags, regnode *val, U32 depth)
+STATIC U32	S_join_exact(pTHX_ struct RExC_state_t *pRExC_state, regnode *scan, UV *min_subtract, bool *has_exactf_sharp_s, U32 flags, regnode *val, U32 depth)
 			__attribute__nonnull__(pTHX_1)
 			__attribute__nonnull__(pTHX_2)
 			__attribute__nonnull__(pTHX_3)
 			__attribute__nonnull__(pTHX_4);
 #define PERL_ARGS_ASSERT_JOIN_EXACT	\
-	assert(pRExC_state); assert(scan); assert(min_change); assert(has_exactf_sharp_s)
+	assert(pRExC_state); assert(scan); assert(min_subtract); assert(has_exactf_sharp_s)
 
 STATIC I32	S_make_trie(pTHX_ struct RExC_state_t *pRExC_state, regnode *startbranch, regnode *first, regnode *last, regnode *tail, U32 word_count, U32 flags, U32 depth)
 			__attribute__nonnull__(pTHX_1)
diff --git a/regcomp.c b/regcomp.c
index 817ffabe2e..391ca61c3d 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -2517,9 +2517,9 @@ S_make_trie_failtable(pTHX_ RExC_state_t *pRExC_state, regnode *source,  regnode
  * The adjacent nodes actually may be separated by NOTHING kind nodes, and
  * these get optimized out
  *
- * If there are problematic code sequences, *min_change is set to the delta
- * that the minimum size of the node can be off from its actual size.  And, the
- * node type of the result is changed to reflect that it contains these
+ * If there are problematic code sequences, *min_subtract is set to the delta
+ * that the minimum size of the node can be less than its actual size.  And,
+ * the node type of the result is changed to reflect that it contains these
  * sequences.
  *
  * And *has_exactf_sharp_s is set to indicate if the node is EXACTF and
@@ -2555,11 +2555,12 @@ S_make_trie_failtable(pTHX_ RExC_state_t *pRExC_state, regnode *source,  regnode
  * There are a number of components to the approach (a lot of work for just
  * three code points!):
  * 1)   This routine examines each EXACTFish node that could contain the
- *      problematic sequences, and if found, returns in *min_change the total
- *      delta between the actual length of the string and one that could match
- *      it.  This delta is used by the caller to adjust the min length of the
- *      match, and the delta between min and max, so that the optimizer doesn't
- *      reject these possibilities based on size constraints
+ *      problematic sequences.  It returns in *min_subtract how much to
+ *      subtract from the the actual length of the string to get a real minimum
+ *      for one that could match it.  This number is usually 0 except for the
+ *      problematic sequences.  This delta is used by the caller to adjust the
+ *      min length of the match, and the delta between min and max, so that the
+ *      optimizer doesn't reject these possibilities based on size constraints.
  * 2)   These sequences are not currently correctly handled by the trie code
  *      either, so it changes the joined node type to ops that are not handled
  *      by trie's, those new ops being EXACTFU_SS and EXACTFU_NO_TRIE.
@@ -2595,22 +2596,23 @@ S_make_trie_failtable(pTHX_ RExC_state_t *pRExC_state, regnode *source,  regnode
  *      cases are either 1-1 folds when no UTF-8 is involved; or is true by
  *      virtue of having this file pre-fold UTF-8 patterns.   I'm
  *      reluctant to try to change this assumption, so instead the code punts.
- *      This routine examines EXACTF nodes for the sharp s, and returns whether
- *      the node is an EXACTF node that contains one or not.  When it is true,
- *      the caller sets a flag that later causes the optimizer in this file to
- *      not set values for the floating and fixed string lengths, and thus
- *      avoid the optimizer code in regexec.c that makes this invalid
- *      assumption.  Thus, there is no optimization based on string lengths for
- *      EXACTF nodes that contain the sharp s.  This only happens for /id rules
- *      (which means the pattern isn't in UTF-8).
+ *      This routine examines EXACTF nodes for the sharp s, and returns a
+ *      boolean indicating whether or not the node is an EXACTF node that
+ *      contains a sharp s.  When it is true, the caller sets a flag that later
+ *      causes the optimizer in this file to not set values for the floating
+ *      and fixed string lengths, and thus avoids the optimizer code in
+ *      regexec.c that makes the invalid assumption.  Thus, there is no
+ *      optimization based on string lengths for EXACTF nodes that contain the
+ *      sharp s.  This only happens for /id rules (which means the pattern
+ *      isn't in UTF-8).
  */
 
-#define JOIN_EXACT(scan,min_change,has_exactf_sharp_s, flags) \
+#define JOIN_EXACT(scan,min_subtract,has_exactf_sharp_s, flags) \
     if (PL_regkind[OP(scan)] == EXACT) \
-        join_exact(pRExC_state,(scan),(min_change),has_exactf_sharp_s, (flags),NULL,depth+1)
+        join_exact(pRExC_state,(scan),(min_subtract),has_exactf_sharp_s, (flags),NULL,depth+1)
 
 STATIC U32
-S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, IV *min_change, bool *has_exactf_sharp_s, U32 flags,regnode *val, U32 depth) {
+S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, UV *min_subtract, bool *has_exactf_sharp_s, U32 flags,regnode *val, U32 depth) {
     /* Merge several consecutive EXACTish nodes into one. */
     regnode *n = regnext(scan);
     U32 stringok = 1;
@@ -2688,7 +2690,7 @@ S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, IV *min_change, boo
 #endif
     }
 
-    *min_change = 0;
+    *min_subtract = 0;
     *has_exactf_sharp_s = FALSE;
 
     /* Here, all the adjacent mergeable EXACTish nodes have been merged.  We
@@ -2777,7 +2779,7 @@ S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, IV *min_change, boo
 			     * for 'ss' */
 			    && OP(scan) != EXACTFL && OP(scan) != EXACTFA)
 			{
-			    *min_change -= 1;
+			    *min_subtract += 1;
 			    OP(scan) = EXACTFU_SS;
 			    s++;    /* No need to look at this character again */
 			}
@@ -2801,7 +2803,7 @@ S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, IV *min_change, boo
 			    break;
 			}
 		      greek_sequence:
-			*min_change -= 4;
+			*min_subtract += 4;
 
 			/* This can't currently be handled by trie's, so change
 			 * the node type to indicate this.  If EXACTFA and
@@ -2834,7 +2836,7 @@ S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, IV *min_change, boo
 			if (s_end - s > 1
 			    && ((*(s+1) & S_or_s_mask) == s_masked))
 			{
-			    *min_change -= 1;
+			    *min_subtract += 1;
 
 			    /* EXACTF nodes need to know that the minimum
 			     * length changed so that a sharp s in the string
@@ -2971,12 +2973,14 @@ S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp,
 
   fake_study_recurse:
     while ( scan && OP(scan) != END && scan < last ){
-        IV min_change = 0;
+        UV min_subtract = 0;    /* How much to subtract from the minimum node
+                                   length to get a real minimum (because the
+                                   folded version may be shorter) */
 	bool has_exactf_sharp_s = FALSE;
 	/* Peephole optimizer: */
 	DEBUG_STUDYDATA("Peep:", data,depth);
 	DEBUG_PEEP("Peep",scan,depth);
-        JOIN_EXACT(scan,&min_change, &has_exactf_sharp_s, 0);
+        JOIN_EXACT(scan,&min_subtract, &has_exactf_sharp_s, 0);
 
 	/* Follow the next-chain of the current node and optimize
 	   away all the NOTHINGs from it.  */
@@ -3493,18 +3497,18 @@ S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp,
 	    else if (has_exactf_sharp_s) {
 		RExC_seen |= REG_SEEN_EXACTF_SHARP_S;
 	    }
-	    min += l + min_change;
+	    min += l - min_subtract;
             if (min < 0) {
                 min = 0;
             }
-            delta += abs(min_change);
+            delta += min_subtract;
 	    if (flags & SCF_DO_SUBSTR) {
-		data->pos_min += l + min_change;
+		data->pos_min += l - min_subtract;
 		if (data->pos_min < 0) {
                     data->pos_min = 0;
                 }
-                data->pos_delta += abs(min_change);
-		if (min_change) {
+                data->pos_delta += min_subtract;
+		if (min_subtract) {
 		    data->longest = &(data->longest_float);
 		}
 	    }