X xbtree: Less copy/garbage in RangedKeySet ops

rebuild tests ~75 -> ~73s.

wcfs/.gitignore

 /wcfs
+*.test

wcfs/internal/xbtree/rangeset.go

@@ -34,7 +34,7 @@ type KeyRange struct {
 	hi_ Key // NOTE _not_ hi) to avoid overflow at ∞;  hi = hi_ + 1
 }
 
-// RangedKeySet is set of Keys with adjacent keys coaleced into Ranges.
+// RangedKeySet is set of Keys with adjacent keys coalesced into Ranges.
 //
 // Zero value represents empty set.
 type RangedKeySet struct {
@@ -109,20 +109,14 @@ func (S *RangedKeySet) AddRange(r KeyRange) {
 	if (jhi - ilo) > 1 {
 		lo  := S.rangev[ilo].lo
 		hi_ := S.rangev[jhi-1].hi_
-		S.rangev = append(
-			S.rangev[:ilo],		append([]KeyRange{
-			KeyRange{lo, hi_}},
-			S.rangev[jhi:]...)...)
+		vReplaceSlice(&S.rangev, ilo,jhi, KeyRange{lo,hi_})
 		debugfRSet("\tmerge S[%d:%d]\t-> %s\n", ilo, jhi, S)
 	}
 	jhi = -1 // no longer valid
 
 	// if [r.lo,r.hi) was outside of any entry - create new entry
 	if r.hi_ < S.rangev[ilo].lo {
-		S.rangev = append(
-			S.rangev[:ilo],		append([]KeyRange{
-			r},
-			S.rangev[ilo:]...)...)
+		vInsert(&S.rangev, ilo, r)
 		debugfRSet("\tinsert %s\t-> %s\n", r, S)
 	}
 
@@ -140,20 +134,16 @@ func (S *RangedKeySet) AddRange(r KeyRange) {
 	// and check if we should merge it with right/left neighbours
 	if ilo+1 < len(S.rangev) { // right
 		if S.rangev[ilo].hi_+1 == S.rangev[ilo+1].lo {
-			S.rangev = append(
-				S.rangev[:ilo],		append([]KeyRange{
-				KeyRange{S.rangev[ilo].lo, S.rangev[ilo+1].hi_}},
-				S.rangev[ilo+2:]...)...)
+			vReplaceSlice(&S.rangev, ilo,ilo+2,
+				KeyRange{S.rangev[ilo].lo, S.rangev[ilo+1].hi_})
 			debugfRSet("\tmerge right\t-> %s\n", S)
 		}
 	}
 
 	if ilo > 0 { // left
 		if S.rangev[ilo-1].hi_+1 == S.rangev[ilo].lo {
-			S.rangev = append(
-				S.rangev[:ilo-1],	append([]KeyRange{
-				KeyRange{S.rangev[ilo-1].lo, S.rangev[ilo].hi_}},
-				S.rangev[ilo+1:]...)...)
+			vReplaceSlice(&S.rangev, ilo-1,ilo+1,
+				KeyRange{S.rangev[ilo-1].lo, S.rangev[ilo].hi_})
 			debugfRSet("\tmerge left\t-> %s\n", S)
 		}
 	}
@@ -204,38 +194,27 @@ func (S *RangedKeySet) DelRange(r KeyRange) {
 	}
 
 	// [ilo+1:jhi-1] should be deleted
-	// [ilo] and [jhi-1] overlap with [r.lo,r.hi) - they shuold be deleted, or shrinked,
+	// [ilo] and [jhi-1] overlap with [r.lo,r.hi) - they should be deleted, or shrinked,
 	// or split+shrinked if ilo==jhi-1 and r is inside [ilo]
 	if jhi-ilo == 1 && S.rangev[ilo].lo < r.lo && r.hi_ < S.rangev[ilo].hi_ {
 		x := S.rangev[ilo]
-		S.rangev = append(
-			S.rangev[:ilo],		append([]KeyRange{
-			x, x},
-			S.rangev[ilo+1:]...)...)
+		vInsert(&S.rangev, ilo, x)
 		jhi++
 		debugfRSet("\tpresplit copy %s\t-> %s\n", x, S)
 	}
 	if S.rangev[ilo].lo < r.lo { // shrink left
-		S.rangev = append(
-			S.rangev[:ilo],		append([]KeyRange{
-			KeyRange{S.rangev[ilo].lo, r.lo-1}},
-			S.rangev[ilo+1:]...)...)
+		S.rangev[ilo] = KeyRange{S.rangev[ilo].lo, r.lo-1}
 		ilo++
 		debugfRSet("\tshrink [%d] left\t-> %s\n", ilo, S)
 	}
 	if r.hi_ < S.rangev[jhi-1].hi_ { // shrink right
-		S.rangev = append(
-			S.rangev[:jhi-1],	append([]KeyRange{
-			KeyRange{r.hi_+1, S.rangev[jhi-1].hi_}},
-			S.rangev[jhi:]...)...)
+		S.rangev[jhi-1] = KeyRange{r.hi_+1, S.rangev[jhi-1].hi_}
 		jhi--
 		debugfRSet("\tshrink [%d] right\t-> %s\n", jhi-1, S)
 	}
 
 	if (jhi - ilo) > 0 {
-		S.rangev = append(
-			S.rangev[:ilo],
-			S.rangev[jhi:]...)
+		vDeleteSlice(&S.rangev, ilo,jhi)
 		debugfRSet("\tdelete S[%d:%d]\t-> %s\n", ilo, jhi, S)
 	}
 
@@ -414,3 +393,32 @@ func debugfRSet(format string, argv ...interface{}) {
 	}
 	fmt.Printf(format, argv...)
 }
+
+
+// ---- slice ops ----
+
+// vInsert inserts r into *pv[i].
+func vInsert(pv *[]KeyRange, i int, r KeyRange) {
+	v := *pv
+	v = append(v, KeyRange{})
+	copy(v[i+1:], v[i:])
+	v[i] = r
+	*pv = v
+}
+
+// vDeleteSlice deletes *pv[lo:hi].
+func vDeleteSlice(pv *[]KeyRange, lo,hi int) {
+	v := *pv
+	n := copy(v[lo:], v[hi:])
+	v = v[:lo+n]
+	*pv = v
+}
+
+// vReplaceSlice replaces *pv[lo:hi] with r.
+func vReplaceSlice(pv *[]KeyRange, lo,hi int, r KeyRange) {
+	v := *pv
+	n := copy(v[lo+1:], v[hi:])
+	v[lo] = r
+	v = v[:lo+1+n]
+	*pv = v
+}