From fadf5a9782adc8d4d25b040e6feba06f16792386 Mon Sep 17 00:00:00 2001
From: Peter Evans <pevans@activecampaign.com>
Date: Thu, 1 Feb 2018 18:41:01 -0600
Subject: [PATCH] Add decode...code

---
 include/apple2.dec.h |   8 +++
 sources.cmake        |   1 +
 src/apple2.dec.c     | 142 +++++++++++++++++++++++++++++++++++++++++++
 tests/apple2.dec.c   |  73 ++++++++++++++++++++++
 4 files changed, 224 insertions(+)
 create mode 100644 include/apple2.dec.h
 create mode 100644 src/apple2.dec.c
 create mode 100644 tests/apple2.dec.c

diff --git a/include/apple2.dec.h b/include/apple2.dec.h
new file mode 100644
index 0000000..d9a4e72
--- /dev/null
+++ b/include/apple2.dec.h
@@ -0,0 +1,8 @@
+#ifndef _APPLE2_DEC_H_
+#define _APPLE2_DEC_H_
+
+#include "vm_segment.h"
+
+extern int apple2_dec_sector(vm_segment *, vm_segment *, int, int);
+
+#endif
diff --git a/sources.cmake b/sources.cmake
index 29fb6a4..1f2b6a5 100644
--- a/sources.cmake
+++ b/sources.cmake
@@ -3,6 +3,7 @@ set(erc_sources
 	apple2.bank.c
 	apple2.dbuf.c
 	apple2.dd.c
+	apple2.dec.c
 	apple2.draw.c
 	apple2.enc.c
 	apple2.kb.c
diff --git a/src/apple2.dec.c b/src/apple2.dec.c
new file mode 100644
index 0000000..4530242
--- /dev/null
+++ b/src/apple2.dec.c
@@ -0,0 +1,142 @@
+/*
+ * apple2.dec.c
+ */
+
+#include "vm_segment.h"
+
+static vm_8bit table[] = {
+    0x68, 0xa2, 0x5e, 0x5f, 0xff, 0x7f, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x20, 0xa2, 0x5e, 0x5f, 0xff, 0x7f, 0x00, 0x00, 0x49, 0x62, 0x4f, 0x10, 0x01, 0x00, 0x00, 0x00,
+    0x40, 0xa2, 0x5e, 0x5f, 0xff, 0x7f, 0x00, 0x00, 0x40, 0xa2, 0x5e, 0x5f, 0xff, 0x7f, 0x00, 0x00,
+    0x58, 0xa2, 0x5e, 0x5f, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x50, 0x61, 0x00, 0x01, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x20, 0x55, 0x4f, 0x10, 0x01, 0x00, 0x00, 0x00,
+    0xc0, 0x54, 0x4f, 0x10, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+};
+
+#if 0
+/*
+ * This is the "reverse" gcr table from enc.c; given one of the disk
+ * bytes, this table can turn them back into a 6-bit byte.
+ */
+static vm_8bit rev62[] = {
+//  00    01    02    03    04    05    06    07    08    09    0a    0b    0c    0d    0e    0f 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 00
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 10
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 20
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 30
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 40
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 50
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 60
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 70
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 80
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x02, 0x03, 0x00, 0x04, 0x05, 0x06, // 90
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x07, 0x08, 0x00, 0x00, 0x00, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, // a0
+    0x00, 0x00, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x00, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, // b0
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1b, 0x00, 0x1c, 0x1e, 0x1e, // c0
+    0x00, 0x00, 0x00, 0x1f, 0x00, 0x00, 0x20, 0x21, 0x00, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, // d0
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x29, 0x2a, 0x2b, 0x00, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, // e0
+    0x00, 0x00, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x00, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, // f0
+};
+#endif
+
+#if 0
+int
+apple2_dec_sector(vm_segment *dest, vm_segment *src, int doff, int soff)
+{
+    int i, orig;
+    vm_8bit xoff;
+    vm_8bit conv[0x157], xor[0x156];
+    vm_8bit lval;
+
+    orig = doff;
+
+    for (i = 0; i < 0x157; i++) {
+        conv[i] = table[vm_segment_get(src, soff + i) & 0x7f];
+    }
+
+    for (i = 0, lval = 0; i < 0x156; i++) {
+        xor[i] = lval ^ conv[i];
+        lval = xor[i];
+    }
+
+    xoff = 0xac;
+    i = 0;
+    while (xoff != 0x02) {
+        if (xoff >= 0xac) {
+            vm_segment_set(dest, doff + xoff, 
+                           (xor[xoff + 0x56] & 0xfc) | ((xor[i] & 0x80) >> 7) | ((xor[i] & 0x40) >> 5));
+        }
+
+        xoff -= 0x56;
+        vm_segment_set(dest, doff + xoff,
+                       (xor[xoff + 0x56] & 0xfc) | ((xor[i] & 0x20) >> 5) | ((xor[i] & 0x10) >> 3));
+
+        xoff -= 0x56;
+        vm_segment_set(dest, doff + xoff,
+                       (xor[xoff + 0x56] & 0xfc) | ((xor[i] & 0x08) >> 3) | ((xor[i] & 0x04) >> 1));
+
+        xoff -= 0x53;
+        i++;
+    }
+
+#if 0
+    for (i = 0; i < 0x56; i++) {
+        vm_8bit vac, v56, v00, 
+                offac, off56;
+
+        offac = i + 0xAC;
+        off56 = i + 0x56;
+
+        vac = (xor[offac + 0x56] & 0xfc) | ((xor[i] & 0x80) >> 7) | ((xor[i] & 0x40) >> 5);
+        v56 = (xor[off56 + 0x56] & 0xfc) | ((xor[i] & 0x20) >> 5) | ((xor[i] & 0x10) >> 3);
+        v00 = (xor[i + 0x56] & 0xfc) | ((xor[i] & 0x08) >> 3) | ((xor[i] & 0x04) >> 1);
+
+        if (i == 0) {
+            printf("vac = %02x, v56 = %02x, v00 = %02x\n", vac, v56, v00);
+        }
+
+        if (offac > 0xAC) {
+            vm_segment_set(dest, doff + offac, vac);
+        }
+
+        vm_segment_set(dest, doff + off56, v56);
+        vm_segment_set(dest, doff + i, v00);
+    }
+#endif
+
+    return 256;
+}
+#endif
+
+int
+apple2_dec_sector(vm_segment *dest, vm_segment *src, int doff, int soff)
+{
+    vm_8bit data[500];
+    int i;
+
+    int prologue = soff;
+    int epilogue = soff + 9 + 0x157;
+
+    // Let's validate that there's really a sector where we think
+    // there's one.
+    if (vm_segment_get(src, prologue) != 0xd5 ||
+        vm_segment_get(src, prologue + 1) != 0xaa ||
+        vm_segment_get(src, prologue + 2) != 0xad ||
+        vm_segment_get(src, epilogue) != 0xde ||
+        vm_segment_get(src, epilogue + 1) != 0xaa ||
+        vm_segment_get(src, epilogue + 2) != 0xeb
+       ) {
+        return 0;
+    }
+
+    // We want to start with just the data field from the encoded
+    // sector; this means stripping out any metadata and self-sync
+    // bytes.
+    for (i = soff + 9; i < epilogue; i++) {
+        data[i - soff - 9] = vm_segment_get(src, i);
+    }
+    
+    return 256;
+}
diff --git a/tests/apple2.dec.c b/tests/apple2.dec.c
new file mode 100644
index 0000000..6110ce7
--- /dev/null
+++ b/tests/apple2.dec.c
@@ -0,0 +1,73 @@
+#include <criterion/criterion.h>
+
+#include "apple2.dec.h"
+
+#if 0
+/*
+ * Ripped from apple2.enc.c
+ */
+static vm_8bit f_sector[] = {
+    0xdd, 0xab, 0xce, 0xd9, 0xc3, 0xf6, 0xdd, 0x77, 0x0e, 0x60, 0x6d, 0x95, 0xbd, 0xe3, 0x74, 0xc0,
+    0xd4, 0xa7, 0x3f, 0xc2, 0x39, 0x37, 0xfa, 0xa7, 0xd1, 0xa9, 0xc9, 0x5e, 0xd3, 0x28, 0x47, 0x04,
+    0x4f, 0xec, 0xfc, 0xc1, 0x5e, 0x90, 0x9a, 0x7d, 0x72, 0x36, 0xd0, 0x23, 0x90, 0xe5, 0x18, 0xeb,
+    0x8a, 0x80, 0xad, 0xda, 0x85, 0xe4, 0xe3, 0x34, 0x72, 0x5c, 0x51, 0x18, 0xf0, 0xec, 0x3f, 0xcf,
+    0xf7, 0xc1, 0x61, 0xe7, 0xad, 0x78, 0xea, 0x8a, 0xa1, 0x53, 0xbc, 0x05, 0x06, 0x77, 0x40, 0xb1,
+    0xfb, 0x21, 0xf4, 0xec, 0x7a, 0xd3, 0xee, 0xcd, 0x99, 0xfa, 0x95, 0x39, 0xf8, 0xe8, 0x2d, 0xf5,
+    0x40, 0x1a, 0x68, 0x0b, 0x7e, 0x96, 0x4c, 0x05, 0x03, 0x74, 0xa9, 0xca, 0x1d, 0x30, 0xf0, 0x96,
+    0x7d, 0xe9, 0x24, 0xca, 0x6b, 0x09, 0x50, 0x69, 0x35, 0xe0, 0x1b, 0xd8, 0xfb, 0x62, 0x47, 0xe6,
+    0x6a, 0xad, 0x3a, 0xd2, 0x5c, 0xe6, 0xda, 0x5f, 0x62, 0xfb, 0x02, 0x61, 0x2b, 0x42, 0x7a, 0x44,
+    0xa2, 0x2f, 0x97, 0xe5, 0x08, 0xc7, 0xf6, 0xe1, 0x7a, 0xd6, 0x6a, 0xc0, 0x11, 0xd6, 0xa4, 0x26,
+    0xac, 0xe4, 0xfb, 0xf3, 0x28, 0x8a, 0x3b, 0x1b, 0x4c, 0x9c, 0x84, 0x55, 0x73, 0x4b, 0x4f, 0xc1,
+    0x0a, 0xd8, 0x9e, 0xdc, 0x1b, 0x01, 0xec, 0x12, 0x41, 0x84, 0x15, 0x8c, 0xb9, 0x29, 0x5f, 0x34,
+    0x99, 0x3e, 0x3b, 0xa8, 0xcf, 0x7c, 0x65, 0x6f, 0x60, 0x45, 0x73, 0xe4, 0xea, 0x84, 0x84, 0x8b,
+    0xaa, 0x46, 0x72, 0xbc, 0xd2, 0x65, 0xbe, 0x5b, 0x2d, 0x24, 0xd6, 0x41, 0x88, 0xd0, 0x6a, 0x80,
+    0x1e, 0x22, 0x7a, 0x44, 0x70, 0x17, 0x44, 0x18, 0x1f, 0x31, 0x41, 0xf5, 0xa0, 0xae, 0x1b, 0xe1,
+    0x4f, 0x9f, 0xdb, 0x5a, 0x74, 0x90, 0x55, 0xe1, 0x49, 0xbf, 0x2d, 0x20, 0xd6, 0x03, 0x03, 0xa2,
+};
+#endif
+
+/*
+ * Same as above -- ripped from apple2.enc.c
+ */
+static vm_8bit f_enc_sector[] = {
+    0xd5, 0xaa, 0xad, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf5, 0xaf, 0x9a, 0xd3, 0xfd, 0xb6, 0xcb,
+    0xb5, 0xfa, 0xb5, 0xe6, 0xb9, 0xf3, 0xea, 0xe7, 0xd6, 0xdb, 0xad, 0xb9, 0xfe, 0xe7, 0xfd, 0xeb,
+    0xfa, 0xee, 0xf3, 0xe9, 0xb7, 0xfa, 0xde, 0xcb, 0xf6, 0xcb, 0xcb, 0x96, 0xfa, 0xec, 0xaf, 0xaf,
+    0xcb, 0xcb, 0xf7, 0xee, 0xec, 0xd3, 0xd9, 0xbb, 0xf6, 0xd9, 0xab, 0xbf, 0xcb, 0xcb, 0xb2, 0xa6,
+    0xcb, 0x97, 0xf4, 0xf5, 0xac, 0xed, 0xb9, 0xad, 0xae, 0xdf, 0xce, 0xe9, 0xb5, 0xb5, 0x9f, 0xab,
+    0xe9, 0xbc, 0x9e, 0xde, 0x9a, 0xb3, 0xb6, 0xd3, 0xdd, 0xbe, 0xd7, 0xb2, 0xd6, 0xb5, 0xac, 0xfc,
+    0xce, 0xbe, 0x9e, 0x9f, 0xaf, 0xac, 0xe6, 0xcf, 0xcb, 0x9b, 0xfe, 0xac, 0xbc, 0xdc, 0xea, 0x9e,
+    0xcd, 0xdd, 0xff, 0xfe, 0x9b, 0xf2, 0xbc, 0xce, 0xcf, 0xbd, 0xdc, 0xda, 0xfe, 0xcb, 0xb4, 0xb6,
+    0xdf, 0x9d, 0xb3, 0xde, 0xf2, 0x9a, 0xf9, 0x9b, 0xb5, 0xf9, 0xfc, 0xe9, 0xce, 0xff, 0xfc, 0xbd,
+    0x9a, 0xad, 0xce, 0xbc, 0xbd, 0x97, 0xf4, 0xb5, 0xad, 0x9b, 0xb6, 0xfa, 0xa6, 0xf3, 0xfc, 0xb2,
+    0xaf, 0xdf, 0xd7, 0xb6, 0xf4, 0xdb, 0xbd, 0xac, 0xfc, 0xfb, 0xeb, 0x96, 0xcd, 0xaf, 0xfc, 0xb6,
+    0xf5, 0xf4, 0x9f, 0xdc, 0xe6, 0xb3, 0xa7, 0xba, 0xbd, 0xcb, 0xe7, 0xed, 0x9d, 0xee, 0xf5, 0xea,
+    0xbb, 0xcd, 0xbd, 0xce, 0xfa, 0xf5, 0xb6, 0x97, 0xce, 0xf6, 0xbd, 0xf4, 0xad, 0xed, 0xbe, 0xfa,
+    0xdc, 0xf2, 0xfb, 0xdf, 0xbd, 0xbb, 0xb2, 0xbc, 0xf4, 0xfe, 0xed, 0xa7, 0xdd, 0xab, 0xdf, 0xda,
+    0xee, 0xdc, 0xfa, 0xda, 0xeb, 0xb3, 0xd7, 0xb3, 0xdd, 0xfe, 0xbd, 0xb6, 0xbf, 0xb2, 0xb3, 0xf9,
+    0xda, 0xeb, 0xcd, 0xfb, 0xf2, 0xae, 0x9e, 0xdd, 0xe7, 0xec, 0xe6, 0xf3, 0xee, 0xcd, 0xd6, 0xd9,
+    0xb6, 0xa6, 0x9a, 0xf5, 0xdf, 0xe9, 0xa7, 0xba, 0xf3, 0x9f, 0xf3, 0xab, 0xb2, 0x97, 0xda, 0xef,
+    0xf3, 0xb5, 0xb4, 0xee, 0x9f, 0xfb, 0xff, 0xb9, 0xee, 0xdb, 0xdd, 0xaf, 0xdb, 0xce, 0xbf, 0xe7,
+    0xe5, 0x97, 0xdb, 0xbe, 0xe9, 0x9f, 0x9a, 0x9b, 0xab, 0xaf, 0xdc, 0x9b, 0xcb, 0x96, 0x9b, 0xa7,
+    0xfb, 0xaf, 0xf2, 0xcb, 0xea, 0xf5, 0xf9, 0xce, 0x9a, 0xfc, 0xdc, 0xef, 0xbb, 0xeb, 0xfa, 0xde,
+    0xb3, 0xbb, 0xb3, 0xaf, 0xbe, 0xb9, 0xbc, 0x97, 0xad, 0xcd, 0xea, 0xba, 0x9b, 0xea, 0xfe, 0xe7,
+    0xf3, 0xb5, 0xd6, 0xad, 0xf9, 0xee, 0xea, 0xe6, 0xfd, 0xdb, 0x9b, 0xfd, 0xf4, 0x96, 0xdf, 0xdf,
+    0xde, 0xaa, 0xeb, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+};
+
+Test(apple2_dec, sector)
+{
+    vm_segment *src, *dest;
+
+    src = vm_segment_create(1000);
+    dest = vm_segment_create(1000);
+
+    vm_segment_copy_buf(src, f_enc_sector, 0, 0, 382);
+
+    printf("it's %d\n", apple2_dec_sector(dest, src, 0, 9));
+
+    for (int i = 0; i < 256; i++) {
+        printf("%02x\n", vm_segment_get(dest, i));
+    }
+}