Refactor magic array size into documented constant

libtwtxt.go

@@ -49,6 +49,12 @@ import (
 	"unsafe"
 )
 
+// arraySize is a fairly large (hopefully large enough) array size for C-backed
+// Go arrays. Unfortunately, it is impossible to use non-constant array bounds
+// in Go, so we cannot specify the real array size but have to use this static
+// one. We're very careful to not exceed the real array bounds, though.
+const arraySize = 1<<30 - 1
+
 //export parse_file
 func parse_file(input *C.char, twter *C.struct_twter) (*C.struct_twt_file, *C.char) {
 	s := strings.NewReader(C.GoString(input))
@@ -80,7 +86,7 @@ func parse_file(input *C.char, twter *C.struct_twter) (*C.struct_twt_file, *C.ch
 	twtsPtr := C.malloc(C.size_t(len(file.Twts())) * C.size_t(unsafe.Sizeof(uintptr(0))))
 
     // convert the C array to a Go array so we can index it
-    a := (*[1<<30 - 1]*C.struct_twt)(twtsPtr)
+    a := (*[arraySize]*C.struct_twt)(twtsPtr)
 
     for i, twt := range file.Twts() {
 //		a[i].twter = convertTwter(twt.Twter())
@@ -125,7 +131,7 @@ func freeTwter(t *C.struct_twter) {
 
 func freeTwters(t *C.struct_twter, length C.int) {
 	if t != nil {
-		twters := (*[1<<30 - 1]*C.struct_twter)(unsafe.Pointer(t))
+		twters := (*[arraySize]*C.struct_twter)(unsafe.Pointer(t))
 		for i := 0; i < int(length); i++ {
 			freeTwter(twters[i])
 		}
@@ -146,7 +152,7 @@ func convertTwt(t types.Twt) *C.struct_twt {
 	}
 
 	mentionsPtr := C.malloc(C.size_t(len(t.Mentions())) * C.size_t(unsafe.Sizeof(uintptr(0))))
-	mentions := (*[1<<30 - 1]*C.struct_twter)(mentionsPtr)
+	mentions := (*[arraySize]*C.struct_twter)(mentionsPtr)
 	for i, mention := range t.Mentions() {
 		mentions[i] = convertTwter(mention.Twter())
 	}
@@ -154,7 +160,7 @@ func convertTwt(t types.Twt) *C.struct_twt {
 	twt.mentions_len = C.int(len(t.Mentions()))
 
 	linksPtr := C.malloc(C.size_t(len(t.Links())) * C.size_t(unsafe.Sizeof(uintptr(0))))
-    links := (*[1<<30 - 1]*C.struct_link)(linksPtr)
+    links := (*[arraySize]*C.struct_link)(linksPtr)
 	for i, link := range t.Links() {
 		links[i] = convertLink(link)
 	}
@@ -162,7 +168,7 @@ func convertTwt(t types.Twt) *C.struct_twt {
 	twt.links_len = C.int(len(t.Links()))
 
 	tagsPtr := C.malloc(C.size_t(len(t.Tags())) * C.size_t(unsafe.Sizeof(uintptr(0))))
-	tags := (*[1<<30 - 1]*C.struct_link)(tagsPtr)
+	tags := (*[arraySize]*C.struct_link)(tagsPtr)
 	for i, tag := range t.Tags() {
 		tags[i] = convertLink(tag)
 	}
@@ -187,7 +193,7 @@ func freeTwt(t *C.struct_twt) {
 
 func freeTwts(t *C.struct_twt, length C.int) {
 	if t != nil {
-		twts := (*[1<<30 - 1]*C.struct_twt)(unsafe.Pointer(t))
+		twts := (*[arraySize]*C.struct_twt)(unsafe.Pointer(t))
 		for i := 0; i < int(length); i++ {
 			freeTwt(twts[i])
 		}
@@ -241,7 +247,7 @@ func freeLink(l *C.struct_link) {
 
 func freeLinks(l *C.struct_link, length C.int) {
 	if l != nil {
-		links := (*[1<<30 - 1]*C.struct_link)(unsafe.Pointer(l))
+		links := (*[arraySize]*C.struct_link)(unsafe.Pointer(l))
 		for i := 0; i < int(length); i++ {
 			freeLink(links[i])
 		}