Fix backwards MARC4 MSb order

asander-ccsw · travisgoodspeed · commit e45c05f73d93 · 2026-02-11T17:21:17.000-05:00
diff --git a/gatodecodermarc4.cpp b/gatodecodermarc4.cpp
@@ -37,9 +37,9 @@ void GatoDecoderMarc4::decode(GatoROM *gr) {
     return;
   }
   std::array<unsigned int, 4> counts = {wordsize, nrows, 2, ncols / 16};
-  std::array<int, 4> col_strides = {2, 0, 1, (int)wordsize * 2};
+  std::array<int, 4> col_strides = {-2, 0, 1, (int)wordsize * 2};
   std::array<int, 4> row_strides = {0, 1, 0, 0};
   AffineDecoder<4> root_decode =
-      AffineDecoder(counts, row_strides, col_strides, 0, 0);
+      AffineDecoder(counts, row_strides, col_strides, 0, wordsize*2-2);
   return root_decode.decode(gr);
 }
diff --git a/gatotests/marc4/md5.txt b/gatotests/marc4/md5.txt
@@ -1 +1 @@
-65827eb3a559ac08d86c4a7540f5671d  marc4-topleft-bits.bin
+df36e3ff8ff976bae2202fd0e84848e7  marc4-topleft-bits.bin

Original file line number	Diff line number	Diff line change
`@@ -37,9 +37,9 @@ void GatoDecoderMarc4::decode(GatoROM *gr) {`
`37`	`37`	`return;`
`38`	`38`	`}`
`39`	`39`	`std::array<unsigned int, 4> counts = {wordsize, nrows, 2, ncols / 16};`
`40`		`- std::array<int, 4> col_strides = {2, 0, 1, (int)wordsize * 2};`
	`40`	`+ std::array<int, 4> col_strides = {-2, 0, 1, (int)wordsize * 2};`
`41`	`41`	`std::array<int, 4> row_strides = {0, 1, 0, 0};`
`42`	`42`	`AffineDecoder<4> root_decode =`
`43`		`- AffineDecoder(counts, row_strides, col_strides, 0, 0);`
	`43`	`+ AffineDecoder(counts, row_strides, col_strides, 0, wordsize*2-2);`
`44`	`44`	`return root_decode.decode(gr);`
`45`	`45`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-65827eb3a559ac08d86c4a7540f5671d marc4-topleft-bits.bin`
	`1`	`+df36e3ff8ff976bae2202fd0e84848e7 marc4-topleft-bits.bin`