another string assignment bugfix

src/basic/basic_commands/cmd_let.s

@@ -272,18 +272,35 @@ cmd_let_assign_string_not_text_area:
 
 cmd_let_assign_string_try_reuse:
 
-	// Check if size of both strings equals
+	// Check if we can reuse old string memory
 
+	sec
 	lda DSCPNT+0
-	cmp __FAC1
-	bne cmd_let_assign_string_try_reuse_unsuccesful
+	sbc __FAC1+0
+	bcc cmd_let_assign_string_try_reuse_unsuccesful
+	
+	// If size of both string equals - simply reuse it
 
-	// Size of both string equals, the old one belongs to the string area - simply reuse it
+	beq_16 helper_let_strvarcpy
 
-	jmp helper_let_strvarcpy
+	// Old string is longer - if difference is at least 3 bytes, we can still reuse it
+
+	sbc #$03
+	bcc cmd_let_assign_string_try_reuse_unsuccesful
+
+	// New string is shorter - enought that we can still reuse the old one with a small trick
+/*
+	clc
+	adc DSCPNT+1
+	sta DSCPNT+1
+	bcs !+
+	inc DSCPNT+2
+*/
+	// XXX
+	// XXX implement this part
+	// XXX
 
 cmd_let_assign_string_try_reuse_unsuccesful:
-	// XXX consider another optimization first: parial memory reuse
 
 	// No special case optimization is possible - but first get rid of the old string
 

src/basic/basic_commands/helper_let_strvarcpy_38K.s

@@ -9,7 +9,10 @@
 
 #if CONFIG_MEMORY_MODEL_38K
 
-helper_let_strdesccpy:
+helper_let_strvarcpy:
+
+	// Retrieve pointer to destination
+	// XXX this part is probably not needed
 
 	ldy #$02
 	lda (VARPNT), y

src/basic/basic_commands/helper_let_strvarcpy_46K_50K.s

@@ -19,6 +19,7 @@ helper_let_strvarcpy:
 	sta CPU_R6510
 
 	// Retrieve pointer to destination
+	// XXX this part is probably not needed
 
 	ldy #$02
 	lda (VARPNT), y

src/basic/basic_commands/helper_let_strvarcpy_60K.s

@@ -9,10 +9,13 @@
 
 #if CONFIG_MEMORY_MODEL_60K
 
-helper_let_strdesccpy:
+helper_let_strvarcpy:
 
 	ldx #<VARPNT
 
+	// Retrieve pointer to destination
+	// XXX this part is probably not needed
+
 	ldy #$02
 	jsr peek_under_roms
 	sta DSCPNT+2