cgb_boot: Compress logo with PB8

The logo is compressed using PB8, a form of RLE with unary-coded
run lengths.  Each block representing 8 bytes consists of a control
byte, where each bit (MSB to LSB) is 0 for literal or 1 for repeat
previous, followed by the literals in that block.

PB8 compression is also used in a few NES games.  A variant called
PB16, where 1 means repeat 2 bytes back, is used in the Game Boy
port of 240p Test Suite and in Libbet and the Magic Floor.

Switching from logo-compress RLE to PB8 decreases the compressed
logo data size from 287 bytes to 253 bytes, saving 34 bytes.
The decompression code is also about 10 bytes smaller.

BootROMs/cgb_boot.asm

@@ -532,7 +532,7 @@ TrademarkSymbol:
     db $3c,$42,$b9,$a5,$b9,$a5,$42,$3c
 
 SameBoyLogo:
-    incbin "SameBoyLogo.rle"
+    incbin "SameBoyLogo.pb8"
 
 AnimationColors:
     dw $7FFF ; White
@@ -634,41 +634,55 @@ ReadCGBLogoHalfTile:
     ld a, e
     ret
 
+; LoadTileset using PB8 codec, 2019 Damian Yerrick
+;
+; The logo is compressed using PB8, a form of RLE with unary-coded
+; run lengths.  Each block representing 8 bytes consists of a control
+; byte, where each bit (MSB to LSB) is 0 for literal or 1 for repeat
+; previous, followed by the literals in that block.
+
+SameBoyLogo_dst = $8080
+SameBoyLogo_length = (128 * 24) / 64
+
 LoadTileset:
-; Copy SameBoy Logo
+    ld hl, SameBoyLogo
-    ld de, SameBoyLogo
+    ld de, SameBoyLogo_dst
-    ld hl, $8080
+    ld c, SameBoyLogo_length
-.sameboyLogoLoop
+.pb8BlockLoop:
-    ld a, [de]
+    ; Register map for PB8 decompression
-    inc de
+    ; HL: source address in boot ROM
-
+    ; DE: destination address in VRAM
-    ld b, a
+    ; A: Current literal value
-    and $0f
+    ; B: Repeat bits, terminated by 1000...
-    jr z, .skipLiteral
+    ; C: Number of 8-byte blocks left in this block
-    ld c, a
+    ; Source address in HL lets the repeat bits go straight to B,
-
+    ; bypassing A and avoiding spilling registers to the stack.
-.literalLoop
+    ld b, [hl]
-    ld a, [de]
-    ldi [hl], a
     inc hl
-    inc de
-    dec c
-    jr nz, .literalLoop
-.skipLiteral
-    swap b
-    ld a, b
-    and $0f
-    jr z, .sameboyLogoEnd
-    ld c, a
-    ld a, [de]
-    inc de
 
-.repeatLoop
+    ; Shift a 1 into lower bit of shift value.  Once this bit
-    ldi [hl], a
+    ; reaches the carry, B becomes 0 and the byte is over
-    inc hl
+    scf
+    rl b
+
+.pb8BitLoop:
+    ; If not a repeat, load a literal byte
+    jr c,.pb8Repeat
+    ld a, [hli]
+.pb8Repeat:
+    ; Decompressed data uses colors 0 and 1, so write once, inc twice
+    ld [de], a
+    inc de
+    inc de
+    sla b
+    jr nz, .pb8BitLoop
+
     dec c
-    jr nz, .repeatLoop
+    jr nz, .pb8BlockLoop
-    jr .sameboyLogoLoop
+
+; End PB8 decoding.  The rest uses HL as the destination
+    ld h, d
+    ld l, e
 
 .sameboyLogoEnd
 ; Copy (unresized) ROM logo

BootROMs/pb8.c

@@ -0,0 +1,330 @@
+/*
+
+PB8 compressor and decompressor
+
+Copyright 2019 Damian Yerrick
+
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
+   in a product, an acknowledgment in the product documentation would be
+   appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be
+   misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdbool.h>
+#include <assert.h>
+
+// For setting stdin/stdout to binary mode
+#if defined (__unix__) || (defined (__APPLE__) && defined (__MACH__))
+#include <unistd.h>
+#define fd_isatty isatty
+#elif defined (_WIN32)
+#include <io.h>
+#include <fcntl.h>
+#define fd_isatty _isatty
+#endif
+
+/*
+
+; The logo is compressed using PB8, a form of RLE with unary-coded
+; run lengths.  Each block representing 8 bytes consists of a control
+; byte, where each bit (MSB to LSB) is 0 for literal or 1 for repeat
+; previous, followed by the literals in that block.
+
+SameBoyLogo_dst = $8080
+SameBoyLogo_length = (128 * 24) / 64
+
+LoadTileset:
+    ld hl, SameBoyLogo
+    ld de, SameBoyLogo_dst
+    ld c, SameBoyLogo_length
+.pb8BlockLoop:
+    ; Register map for PB8 decompression
+    ; HL: source address in boot ROM
+    ; DE: destination address in VRAM
+    ; A: Current literal value
+    ; B: Repeat bits, terminated by 1000...
+    ; C: Number of 8-byte blocks left in this block
+    ; Source address in HL lets the repeat bits go straight to B,
+    ; bypassing A and avoiding spilling registers to the stack.
+    ld b, [hl]
+    inc hl
+
+    ; Shift a 1 into lower bit of shift value.  Once this bit
+    ; reaches the carry, B becomes 0 and the byte is over
+    scf
+    rl b
+
+.pb8BitLoop:
+    ; If not a repeat, load a literal byte
+    jr c,.pb8Repeat
+    ld a, [hli]
+.pb8Repeat:
+    ; Decompressed data uses colors 0 and 1, so write once, inc twice
+    ld [de], a
+    inc de
+    inc de
+    sla b
+    jr nz, .pb8BitLoop
+
+    dec c
+    jr nz, .pb8BlockLoop
+    ret
+
+*/
+
+/* Compressor and decompressor *************************************/
+
+/**
+ * Compresses an input stream to PB8 data on an output stream.
+ * @param infp input stream
+ * @param outfp output stream
+ * @param blocklength size of an independent input block in bytes
+ * @return 0 for reaching infp end of file, or EOF for error
+ */
+int pb8(FILE *infp, FILE *outfp, size_t blocklength) {
+  blocklength >>= 3;  // convert bytes to blocks
+  assert(blocklength > 0);
+  while (1) {
+    int last_byte = EOF;  // value that never occurs in a file
+    for (size_t blkleft = blocklength; blkleft > 0; --blkleft) {
+      unsigned int control_byte = 0x0001;
+      unsigned char literals[8];
+      size_t nliterals = 0;
+      while (control_byte < 0x100) {
+        int c = fgetc(infp);
+        if (c == EOF) break;
+
+        control_byte <<= 1;
+        if (c == last_byte) {
+          control_byte |= 0x01;
+        } else {
+          literals[nliterals++] = last_byte = c;
+        }
+      }
+      if (control_byte > 1) {
+        // Fill partial block with repeats
+        while (control_byte < 0x100) {
+          control_byte = (control_byte << 1) | 1;
+        }
+
+        // Write control byte and check for write failure
+        int ok = fputc(control_byte & 0xFF, outfp);
+        if (ok == EOF) return EOF;
+        size_t ok2 = fwrite(literals, 1, nliterals, outfp);
+        if (ok2 < nliterals) return EOF;
+      }
+
+      // If finished, return success or failure
+      if (ferror(infp) || ferror(outfp)) return EOF;
+      if (feof(infp)) return 0;
+    }  // End 8-byte block
+  }  // End packet, resetting last_byte
+}
+
+/**
+ * Decompresses PB8 data on an input stream to an output stream.
+ * @param infp input stream
+ * @param outfp output stream
+ * @return 0 for reaching infp end of file, or EOF for error
+ */
+int unpb8(FILE *infp, FILE *outfp) {
+  int last_byte = 0;
+  while (1) {
+    int control_byte = fgetc(infp);
+    if (control_byte == EOF) {
+      return feof(infp) ? 0 : EOF;
+    }
+    control_byte &= 0xFF;
+    for (size_t bytesleft = 8; bytesleft > 0; --bytesleft) {
+      if (!(control_byte & 0x80)) {
+        last_byte = fgetc(infp);
+        if (last_byte == EOF) return EOF;  // read error
+      }
+      control_byte <<= 1;
+      int ok = fputc(last_byte, outfp);
+      if (ok == EOF) return EOF;
+    }
+  }
+}
+
+/* CLI frontend ****************************************************/
+
+static inline void set_fd_binary(unsigned int fd) {
+#ifdef _WIN32
+  _setmode(fd, _O_BINARY);
+#else
+  (void) fd;
+#endif
+}
+
+static const char *usage_msg =
+"usage: pb8 [-d] [-l blocklength] [infile [outfile]]\n"
+"Compresses a file using RLE with unary run and literal lengths.\n"
+"\n"
+"options:\n"
+"  -d                decompress\n"
+"  -l blocklength    allow RLE packets to span up to blocklength\n"
+"                      input bytes (multiple of 8; default 8)\n"
+"  -h, -?, --help    show this usage page\n"
+"  --version         show copyright info\n"
+"\n"
+"If infile is - or missing, it is standard input.\n"
+"If outfile is - or missing, it is standard output.\n"
+"You cannot compress to or decompress from a terminal.\n"
+;
+static const char *version_msg =
+"PB8 compressor (C version) v0.01\n"
+"Copyright 2019 Damian Yerrick <https://pineight.com/contact/>\n"
+"This software is provided 'as-is', without any express or implied\n"
+"warranty.\n"
+;
+static const char *toomanyfilenames_msg =
+"pb8: too many filenames; try pb8 --help\n";
+
+int main(int argc, char **argv) {
+  const char *infilename = NULL;
+  const char *outfilename = NULL;
+  bool decompress = false;
+  size_t blocklength = 8;
+
+  for (int i = 1; i < argc; ++i) {
+    if (argv[i][0] == '-' && argv[i][1] != 0) {
+      if (!strcmp(argv[i], "--help")) {
+        fputs(usage_msg, stdout);
+        return 0;
+      }
+      if (!strcmp(argv[i], "--version")) {
+        fputs(version_msg, stdout);
+        return 0;
+      }
+
+      // -t1 or -t 1
+      int argtype = argv[i][1];
+      switch (argtype) {
+        case 'h':
+        case '?':
+          fputs(usage_msg, stdout);
+          return 0;
+
+        case 'd':
+          decompress = true;
+          break;
+
+        case 'l': {
+          const char *argvalue = argv[i][2] ? argv[i] + 2 : argv[++i];
+          const char *endptr = NULL;
+
+          unsigned long tvalue = strtoul(argvalue, (char **)&endptr, 10);
+          if (endptr == argvalue || tvalue == 0 || tvalue > SIZE_MAX) {
+            fprintf(stderr, "pb8: block length %s not a positive integer\n",
+                    argvalue);
+            return EXIT_FAILURE;
+          }
+          if (tvalue % 8 != 0) {
+            fprintf(stderr, "pb8: block length %s not a multiple of 8\n",
+                    argvalue);
+            return EXIT_FAILURE;
+          }
+          blocklength = tvalue;
+        } break;
+
+        default:
+          fprintf(stderr, "pb8: unknown option -%c\n", argtype);
+          return EXIT_FAILURE;
+      }
+    } else if (!infilename) {
+      infilename = argv[i];
+    } else if (!outfilename) {
+      outfilename = argv[i];
+    } else {
+      fputs(toomanyfilenames_msg, stderr);
+      return EXIT_FAILURE;
+    }
+  }
+  if (infilename && !strcmp(infilename, "-")) {
+    infilename = NULL;
+  }
+  if (!infilename && decompress && fd_isatty(0)) {
+    fputs("pb8: cannot decompress from terminal; try redirecting stdin\n",
+          stderr);
+    return EXIT_FAILURE;
+  }
+  if (outfilename && !strcmp(outfilename, "-")) {
+    outfilename = NULL;
+  }
+  if (!outfilename && !decompress && fd_isatty(1)) {
+    fputs("pb8: cannot compress to terminal; try redirecting stdout or pb8 --help\n",
+          stderr);
+    return EXIT_FAILURE;
+  }
+
+  FILE *infp = NULL;
+  if (infilename) {
+    infp = fopen(infilename, "rb");
+    if (!infp) {
+      fprintf(stderr, "pb8: error opening %s ", infilename);
+      perror("for reading");
+      return EXIT_FAILURE;
+    }
+  } else {
+    infp = stdin;
+    set_fd_binary(0);
+  }
+
+  FILE *outfp = NULL;
+  if (outfilename) {
+    outfp = fopen(outfilename, "wb");
+    if (!outfp) {
+      fprintf(stderr, "pb8: error opening %s ", outfilename);
+      perror("for writing");
+      fclose(infp);
+      return EXIT_FAILURE;
+    }
+  } else {
+    outfp = stdout;
+    set_fd_binary(1);
+  }
+
+  int compfailed = 0;
+  int has_ferror = 0;
+  if (decompress) {
+    compfailed = unpb8(infp, outfp);
+  } else {
+    compfailed = pb8(infp, outfp, blocklength);
+  }
+  fflush(outfp);
+  if (ferror(infp)) {
+    fprintf(stderr, "pb8: error reading %s\n",
+            infilename ? infilename : "<stdin>");
+    has_ferror = EOF;
+  }
+  fclose(infp);
+  if (ferror(outfp)) {
+    fprintf(stderr, "pb8: error writing %s\n",
+            outfilename ? outfilename : "<stdout>");
+    has_ferror = EOF;
+  }
+  fclose(outfp);
+
+  if (compfailed && !has_ferror) {
+    fputs("pb8: unknown compression failure\n", stderr);
+  }
+
+  return (compfailed || has_ferror) ? EXIT_FAILURE : EXIT_SUCCESS;
+}

Makefile

@@ -13,13 +13,15 @@ ifneq ($(findstring MSYS,$(PLATFORM)),)
 PLATFORM := windows32
 endif
 
-LOGO_COMPRESS := build/logo-compress
-
 ifeq ($(PLATFORM),windows32)
 _ := $(shell chcp 65001)
-LOGO_COMPRESS := build/logo-compress.exe
+EXESUFFIX:=.exe
+else
+EXESUFFIX:=
 endif
 
+PB8_COMPRESS := build/pb8$(EXESUFFIX)
+
 ifeq ($(PLATFORM),Darwin)
 DEFAULT := cocoa
 else
@@ -302,11 +304,11 @@ $(BIN)/tester/sameboy_tester.exe: $(CORE_OBJECTS) $(SDL_OBJECTS)
 $(BIN)/SDL/%.bin $(BIN)/tester/%.bin: $(BOOTROMS_DIR)/%.bin
 	-@$(MKDIR) -p $(dir $@)
 	cp -f $^ $@
-	
+
 $(BIN)/SameBoy.app/Contents/Resources/%.bin: $(BOOTROMS_DIR)/%.bin
 	-@$(MKDIR) -p $(dir $@)
 	cp -f $^ $@
-	
+
 $(BIN)/SDL/LICENSE: LICENSE
 	-@$(MKDIR) -p $(dir $@)
 	cp -f $^ $@
@@ -314,7 +316,7 @@ $(BIN)/SDL/LICENSE: LICENSE
 $(BIN)/SDL/registers.sym: Misc/registers.sym
 	-@$(MKDIR) -p $(dir $@)
 	cp -f $^ $@
-	
+
 $(BIN)/SDL/background.bmp: SDL/background.bmp
 	-@$(MKDIR) -p $(dir $@)
 	cp -f $^ $@
@@ -329,17 +331,17 @@ $(OBJ)/%.1bpp: %.png
 	-@$(MKDIR) -p $(dir $@)
 	rgbgfx -d 1 -h -o $@ $<
 
-$(OBJ)/BootROMs/SameBoyLogo.rle: $(OBJ)/BootROMs/SameBoyLogo.1bpp $(LOGO_COMPRESS)
+$(OBJ)/BootROMs/SameBoyLogo.pb8: $(OBJ)/BootROMs/SameBoyLogo.1bpp $(PB8_COMPRESS)
-	$(realpath $(LOGO_COMPRESS)) < $< > $@
+	$(realpath $(PB8_COMPRESS)) -l 384 $< $@
 
-$(LOGO_COMPRESS): BootROMs/logo-compress.c
+$(PB8_COMPRESS): BootROMs/pb8.c
 	$(CC) $< -o $@
 
 $(BIN)/BootROMs/agb_boot.bin: BootROMs/cgb_boot.asm
 $(BIN)/BootROMs/cgb_boot_fast.bin: BootROMs/cgb_boot.asm
 $(BIN)/BootROMs/sgb2_boot: BootROMs/sgb_boot.asm
 
-$(BIN)/BootROMs/%.bin: BootROMs/%.asm $(OBJ)/BootROMs/SameBoyLogo.rle
+$(BIN)/BootROMs/%.bin: BootROMs/%.asm $(OBJ)/BootROMs/SameBoyLogo.pb8
 	-@$(MKDIR) -p $(dir $@)
 	rgbasm -i $(OBJ)/BootROMs/ -i BootROMs/ -o $@.tmp $<
 	rgblink -o $@.tmp2 $@.tmp
@@ -349,7 +351,7 @@ $(BIN)/BootROMs/%.bin: BootROMs/%.asm $(OBJ)/BootROMs/SameBoyLogo.rle
 # Libretro Core (uses its own build system)
 libretro:
 	$(MAKE) -C libretro
-	
+
 # Clean
 clean:
 	rm -rf build