Some rewording

Author: axic

libyul/backends/wasm/polyfill/Interface.yul

@@ -67,24 +67,27 @@ function calldatacopy(x1, x2, x3, x4, y1, y2, y3, y4, z1, z2, z3, z4) {
 	let cds:i32 := eth.getCallDataSize()
 	let destination:i32 := u256_to_i32(x1, x2, x3, x4)
 	let offset:i32 := u256_to_i32(y1, y2, y3, y4)
-	let size:i32 := u256_to_i32(z1, z2, z3, z4)
-	let copy_size:i32 := size
+	let requested_size:i32 := u256_to_i32(z1, z2, z3, z4)
 	// overflow?
-	if i32.gt_u(offset, i32.sub(0xffffffff:i32, size)) {
+	if i32.gt_u(offset, i32.sub(0xffffffff:i32, requested_size)) {
 		eth.revert(0:i32, 0:i32)
 	}
-	if i32.gt_u(i32.add(offset, size), cds) {
-		copy_size := i32.sub(cds, offset)
+
+	let available_size := i32.sub(cds, offset)
+	if i32.lt_u(offset, cds) {
+		available_size := 0:i32
 	}
-	if i32.gt_u(copy_size, 0:i32) {
+
+	if i32.gt_u(available_size, 0:i32) {
 		eth.callDataCopy(
 			destination,
 			offset,
-			copy_size
+			available_size
 		)
 	}
-	if i32.gt_u(size, copy_size) {
-		memset(i32.add(destination, copy_size), 0:i32, i32.sub(size, copy_size))
+
+	if i32.gt_u(requested_size, available_size) {
+		memset(i32.add(destination, available_size), 0:i32, i32.sub(requested_size, available_size))
 	}
 }