Raise minimum count for iterate to 2 alternate to 3

Sligly saves space but mostly removes overlapping encodings
Rangi42 · Mar 8, 2023 · ca95feb · ca95feb
1 parent 8444a78
commit ca95feb
Show file tree

Hide file tree

Showing 6 changed files with 25 additions and 9 deletions.
diff --git a/home/decompress.asm b/home/decompress.asm
@@ -170,9 +170,6 @@ DEF LZ_LONG_HI       EQU %00000011
 	ld [hli], a
 	pop de
 
-	; assume count >= 3, because < 3 is nonsense
-	dec bc
-	dec bc
 	jr .lz_copy_repeat
 
 .lz_copy
@@ -288,6 +285,7 @@ DEF LZ_LONG_HI       EQU %00000011
 
 .lz_iterate
 	ld a, [de]
+	ld [hli], a
 	inc de
 	jr .fill
 

diff --git a/tools/lz/dpcomp.c b/tools/lz/dpcomp.c
@@ -67,7 +67,8 @@ void process_input(void) {
         unsigned count = 0;
         do {
             count++;
-            consider(plen, (struct command) {
+            if (!current_byte || count >= 2)
+                consider(plen, (struct command) {
                 .command = current_byte ? LZ_REPEAT : LZ_ZERO,
                 .count = count,
                 .value = current_byte,
@@ -78,7 +79,8 @@ void process_input(void) {
             count = 1;
             do {
                 count++;
-                consider(plen, (struct command) {
+                if (count >= 3)
+                    consider(plen, (struct command) {
                     .command = LZ_ALTERNATE,
                     .count = count,
                     .value = (data[plen - count + 1] << 8) | (data[plen - count]),

diff --git a/tools/lz/output.c b/tools/lz/output.c
@@ -101,11 +101,15 @@ void write_commands_to_file (const char * file, const struct command * commands,
 }
 
 void write_command_to_file (FILE * fp, struct command command, const unsigned char * input_stream) {
-  if ((!command.count) || (command.count > MAX_COMMAND_COUNT)) error_exit(2, "invalid command in output stream");
   unsigned char buf[4];
   unsigned char * pos = buf;
   int n;
-  command.count --;
+
+  command.count -= minimum_count(command.command);
+
+  /* Check for over and under sized commands */
+  if (command.count > MAX_COMMAND_COUNT - 1) error_exit(2, "invalid command in output stream");
+
   if (command.count < SHORT_COMMAND_COUNT)
     *(pos ++) = (command.command << 5) + command.count;
   else {

diff --git a/tools/lz/proto.h b/tools/lz/proto.h
@@ -66,6 +66,7 @@ unsigned char * get_uncompressed_data(const struct command *, const unsigned cha
 // util.c
 noreturn error_exit(int, const char *, ...);
 unsigned char * read_file_into_buffer(const char *, unsigned short *);
+unsigned minimum_count(unsigned command);
 short command_size(struct command);
 unsigned short compressed_length(const struct command *, unsigned short);
 

diff --git a/tools/lz/uncomp.c b/tools/lz/uncomp.c
@@ -20,7 +20,7 @@ struct command * get_commands_from_file (const unsigned char * data, unsigned sh
       if (!(remaining --)) goto error;
       current -> count |= *(rp ++);
     }
-    current -> count ++;
+    current -> count += minimum_count(current -> command);
     switch (current -> command) {
       case LZ_DATA:
         if (remaining <= current -> count) goto error;

diff --git a/tools/lz/util.c b/tools/lz/util.c
@@ -22,8 +22,19 @@ unsigned char * read_file_into_buffer (const char * file, unsigned short * size)
   return buf;
 }
 
+unsigned minimum_count (unsigned command) {
+  switch (command) {
+    case LZ_ALTERNATE:
+        return 3;
+    case LZ_REPEAT:
+        return 2;
+    default:
+        return 1;
+  }
+}
+
 short command_size (struct command command) {
-  short header_size = 1 + (command.count > SHORT_COMMAND_COUNT);
+  short header_size = 1 + (command.count - minimum_count(command.command) > SHORT_COMMAND_COUNT - 1);
   if (command.command & 4) return header_size + 1 + (command.value >= 0);
   return header_size + command.command[(short []) {command.count, 1, 2, 0}];
 }