From c2fad8d3e010c3fadf6101b4efa6903d0d95d9d6 Mon Sep 17 00:00:00 2001
From: Andre Fachat <fachat@web.de>
Date: Fri, 27 Oct 2023 15:00:50 +0200
Subject: [PATCH] dsbexpr

---
 xa/src/xa.c             | 17 +++--------------
 xa/src/xaa.c            | 10 +++++++---
 xa/src/xah.h            |  3 +++
 xa/src/xat.c            |  2 +-
 xa/tests/usb65/Makefile |  5 ++++-
 5 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/xa/src/xa.c b/xa/src/xa.c
index 5c11c08..0f241e7 100644
--- a/xa/src/xa.c
+++ b/xa/src/xa.c
@@ -954,17 +954,6 @@ static void usage(int default816, FILE *fp)
 	    "  --help      display this help and exit\n");
 }
 
-/*
-static char *ertxt[] = { "Syntax","Label definiert",
-          "Label nicht definiert","Labeltabelle voll",
-          "Label erwartet","Speicher voll","Illegaler Opcode",
-          "Falsche Adressierungsart","Branch ausserhalb des Bereichs",
-          "Ueberlauf","Division durch Null","Pseudo-Opcode erwartet",
-          "Block-Stack-Ueberlauf","Datei nicht gefunden",
-          "End of File","Block-Struktur nicht abgeschlossen",
-          "NoBlk","NoKey","NoLine","OKDef","DSB","NewLine",
-          "NewFile","CMOS-Befehl","pp:Falsche Anzahl Parameter" };
-*/
 static char *ertxt[] = {
 	"Syntax",			// E_SYNTAX	=-1
 	"Label already defined",	// E_LABDEF	=-2
@@ -1003,9 +992,9 @@ static char *ertxt[] = {
 	"Illegal quantity",		// E_ILLQUANT	=-35
 	".bin",				// E_BIN	=-36
 	"#error directive",		// E_UERROR	=-37
-	"Assertion",		// E_AERROR	=-38
+	"Assertion",			// E_AERROR	=-38
+	"DSB has negative length",	// E_NEGDSBLEN	=-39
 /* placeholders for future fatal errors */
-		"",			// -39
 		"",			// -40
 		"",			// -41
 		"",			// -42
@@ -1042,7 +1031,7 @@ static char *ertxt[] = {
 	  "Open preprocessor directive at end of file (intentional?)", // W_OPENPP =-72
 	  "Included binary data exceeds 64KB",		// W_OVER64K	=-73
 	  "Included binary data exceeds 16MB",		// W_OVER16M	=-74
-          "MVN/MVP $XXXX syntax is deprecated and will be removed", // W_OLDMVNS =-75
+          "Subtracting pointer from constant not supported in -R mode", // W_SUBTRACT =-75
 /* more placeholders */
 		"",			// -76
 		"",			// -77
diff --git a/xa/src/xaa.c b/xa/src/xaa.c
index 98fff52..db8cc3c 100644
--- a/xa/src/xaa.c
+++ b/xa/src/xaa.c
@@ -201,15 +201,19 @@ printf("pointer: v=%04x, afl=%04x\n",*v,afl);
                {
 		    if(afl || *nafl) {	/* check pointer arithmetic */
 		      if((afl == *nafl) && (afl!=SEG_UNDEFZP) && (afl!=SEG_UNDEF) && o==2) {
-			afl = 0; 	/* substract two pointers */
+			afl = 0; 	/* subtract two pointers */
 		      } else 
 		      if(((afl && !*nafl) || (*nafl && !afl)) && o==1) {
 			afl=(afl | *nafl);  /* add constant to pointer */
 		      } else 
 		      if((afl && !*nafl) && o==2) {
-			afl=(afl | *nafl);  /* substract constant from pointer */
+			afl=(afl | *nafl);  /* subtract constant from pointer */
 		      } else {
-                        /* allow math in the same segment */
+       		        if((!afl && *nafl) && o==2) {
+			  /* subtract pointer from constant */
+			  errout(W_SUBTRACT);
+			}
+                 /* allow math in the same segment */
 			if(segment!=SEG_ABS && segment != afl) { 
 			  if(!dsb_len) {
 			    /*printf("ILLPOINTER=dsb_len=%d,segment=%d\n",dsb_len, segment);*/
diff --git a/xa/src/xah.h b/xa/src/xah.h
index 7b4abfd..8a0b5bb 100644
--- a/xa/src/xah.h
+++ b/xa/src/xah.h
@@ -140,6 +140,8 @@ typedef struct {
 #define E_BIN		-36	/* okdef */
 #define E_UERROR	-37	/* #error */
 #define	E_AERROR	-38	/* .assert failed */
+#define	E_NEGDSBLEN	-39	/* .dsb has negative length */
+
 /* errors thru 64 are placeholders available for use */
 
 #define W_ADRRELOC	-65	/* word relocation in byte value */
@@ -152,6 +154,7 @@ typedef struct {
 #define W_OPENPP	-72	/* warning about open preprocessor directive */
 #define W_OVER64K	-73	/* included binary over 64K in 6502 mode */
 #define W_OVER16M	-74	/* included binary over 16M in 65816 mode */
+#define	W_SUBTRACT	-75	/* subtract a segment pointer from a constant - not supported in -R mode */
 /* warnings 75-77 are placeholders available for use */
 
 /* Meta-values for the token list. Note must not overlap with the
diff --git a/xa/src/xat.c b/xa/src/xat.c
index 86cbf40..52671ea 100644
--- a/xa/src/xat.c
+++ b/xa/src/xat.c
@@ -1623,7 +1623,7 @@ fprintf(stderr, "mvn mvp: %i %i %i %i %i\n", t[0], t[i], wide, i, j);
                if(!(er=a_term(t+1,&j,&i,pc[segment],&afl,&label,0)))
                {
                     if (j<0)
-			er=E_SYNTAX;
+			er=E_NEGDSBLEN;
 		    else
 /*
                     if(t[i+1]!=',')
diff --git a/xa/tests/usb65/Makefile b/xa/tests/usb65/Makefile
index 584b21a..8202be6 100644
--- a/xa/tests/usb65/Makefile
+++ b/xa/tests/usb65/Makefile
@@ -1,7 +1,7 @@
 
 XA=../../xa 
 
-all: test1 test2
+all: test1 test2 test3
 
 test1: test1.a65
 	${XA} -XC -R -U $<
@@ -9,3 +9,6 @@ test1: test1.a65
 test2: test2.a65
 	${XA} -R -U $<
 
+test3: test3.a65
+	${XA} -R -U $<
+