fixed build error on 32bit systems with pointer-to-slice casts

As part of this, these casts were centralized, with an explanation what to do. The compiler most likely inlines them again, anyway.

AllocatedGlyphRanges.go

@@ -31,7 +31,7 @@ func (builder *GlyphRangesBuilder) Build() AllocatedGlyphRanges {
 	const uint16PerRangeEntry = 2
 	ranges := builder.mergedRanges()
 	raw := C.malloc(C.size_t(bytesPerUint16 * ((len(ranges) * uint16PerRangeEntry) + 1)))
-	rawSlice := (*[1 << 30]uint16)(raw)[:]
+	rawSlice := ptrToUint16Slice(raw)
 	outIndex := 0
 	for _, r := range ranges {
 		rawSlice[outIndex+0] = r.from

FontAtlas.go

@@ -103,7 +103,7 @@ func (atlas FontAtlas) AddFontFromMemoryTTFV(
 	}
 
 	fontDataC := C.malloc(C.size_t(len(fontData)))
-	cBuf := (*[1 << 30]byte)(fontDataC)
+	cBuf := ptrToByteSlice(fontDataC)
 
 	copy(cBuf[:], fontData)
 

GlyphRanges.go

@@ -21,7 +21,7 @@ func (glyphs GlyphRanges) extract() (result []glyphRange) {
 	if glyphs == 0 {
 		return
 	}
-	rawSlice := (*[1 << 30]uint16)(unsafe.Pointer(glyphs.handle()))[:]
+	rawSlice := ptrToUint16Slice(unsafe.Pointer(glyphs.handle()))
 	index := 0
 	// iterate until end of list or an arbitrary paranoia limit, should the list not be proper.
 	for (rawSlice[index] != 0) && (index < 1000) {

InputTextCallbackData.go

@@ -125,7 +125,7 @@ func (data InputTextCallbackData) Buffer() []byte {
 		return nil
 	}
 	textLen := data.bufTextLen()
-	return ((*[1 << 30]byte)(unsafe.Pointer(ptr)))[:textLen]
+	return ptrToByteSlice(unsafe.Pointer(ptr))[:textLen]
 }
 
 // MarkBufferModified indicates that the content of the buffer was modified during a callback.

WrapperConverter.go

@@ -77,8 +77,9 @@ func newStringBuffer(initialValue string) *stringBuffer {
 	bufSize := len(rawText) + 1
 	newPtr := C.malloc(C.size_t(bufSize))
 	zeroOffset := bufSize - 1
-	copy(((*[1 << 30]byte)(newPtr))[:zeroOffset], rawText)
-	((*[1 << 30]byte)(newPtr))[zeroOffset] = 0
+	buf := ptrToByteSlice(newPtr)
+	copy(buf[:zeroOffset], rawText)
+	buf[zeroOffset] = 0
 
 	return &stringBuffer{ptr: newPtr, size: bufSize}
 }
@@ -101,7 +102,7 @@ func (buf *stringBuffer) resizeTo(requestedSize int) {
 	if copySize > 0 {
 		C.memcpy(newPtr, buf.ptr, C.size_t(copySize))
 	}
-	((*[1 << 30]byte)(newPtr))[bufSize-1] = 0
+	ptrToByteSlice(newPtr)[bufSize-1] = 0
 	C.free(buf.ptr)
 	buf.ptr = newPtr
 	buf.size = bufSize
@@ -111,6 +112,21 @@ func (buf stringBuffer) toGo() string {
 	if (buf.ptr == nil) || (buf.size < 1) {
 		return ""
 	}
-	((*[1 << 30]byte)(buf.ptr))[buf.size-1] = 0
+	ptrToByteSlice(buf.ptr)[buf.size-1] = 0
 	return C.GoString((*C.char)(buf.ptr))
 }
+
+// unrealisticLargePointer is used to cast an arbitrary native pointer to a slice.
+// Its value is chosen to fit into a 32bit architecture, and still be large
+// enough to cover "any" data blob. Note that this value is in bytes.
+// Should an array of larger primitives be addressed, be sure to divide the value
+// by the size of the elements.
+const unrealisticLargePointer = 1 << 30
+
+func ptrToByteSlice(p unsafe.Pointer) []byte {
+	return (*[unrealisticLargePointer]byte)(p)[:]
+}
+
+func ptrToUint16Slice(p unsafe.Pointer) []uint16 {
+	return (*[unrealisticLargePointer / 2]uint16)(p)[:]
+}