diff --git a/src/apple2.dec.c b/src/apple2.dec.c index 4530242..ea3dc51 100644 --- a/src/apple2.dec.c +++ b/src/apple2.dec.c @@ -2,118 +2,28 @@ * apple2.dec.c */ +#include + #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[] = { +static vm_8bit conv6bit[] = { // 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 + 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, // 00 + 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x04, 0xff, 0xff, 0x08, 0x0c, 0xff, 0x10, 0x14, 0x18, // 10 + 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1c, 0x20, 0xff, 0xff, 0xff, 0x24, 0x28, 0x2c, 0x30, 0x34, // 20 + 0xff, 0xff, 0x38, 0x3c, 0x40, 0x44, 0x48, 0x4c, 0xff, 0x50, 0x54, 0x58, 0x5c, 0x60, 0x64, 0x68, // 30 + 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x6c, 0xff, 0x70, 0x74, 0x78, // 40 + 0xff, 0xff, 0xff, 0x7c, 0xff, 0xff, 0x80, 0x84, 0xff, 0x88, 0x8c, 0x90, 0x94, 0x98, 0x9c, 0xa0, // 50 + 0xff, 0xff, 0xff, 0xff, 0xff, 0xa4, 0xa8, 0xac, 0xff, 0xb0, 0xb4, 0xb8, 0xbc, 0xc0, 0xc4, 0xc8, // 60 + 0xff, 0xff, 0xcc, 0xd0, 0xd4, 0xd8, 0xdc, 0xe0, 0xff, 0xe4, 0xe8, 0xec, 0xf0, 0xf4, 0xf8, 0xfc, // 70 }; -#endif -#if 0 -int +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 conv[0x157]; + vm_8bit 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; @@ -131,12 +41,63 @@ apple2_dec_sector(vm_segment *dest, vm_segment *src, int doff, int soff) 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); + // Here we mean to convert the 6-and-2 encoded bytes back into its + // first intermediate form + for (i = 0; i < 0x157; i++) { + conv[i] = conv6bit[vm_segment_get(src, soff + i + 9) & 0x7f]; } - + + // Originally, we XOR'd each byte when encoding; so we need to do + // another XOR, in pretty much the same manner. + for (i = 0, lval = 0; i < 0x156; i++) { + xor[i] = lval ^ conv[i]; + lval = xor[i]; + } + + // Now we need to copy every byte back into its form that would be + // found on the original disk image. We're using the same sort of + // loop that jumps around three different sections of the array per + // iteration. + for (i = 0; i < 0x56; i++) { + vm_8bit offac, off56; + vm_8bit vac, v56, v00; + + offac = i + 0xac; + off56 = i + 0x56; + + // Recall that the least significant bits are packed into the + // first 86 (0x56) bytes of the 6-and-2 scheme block. So what + // we're doing here is grabbing the 6 _most_ significant bits + // (which is offac + 0x56), then using an OR to pack on the + // least significant bits from the those first 86 bytes. + 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 we wrap around to 00 or 01, as will likely do with offac, + // don't do the set (it gets set with doff+i and v00). + if (offac >= 0xac) { + vm_segment_set(dest, doff + offac, vac); + } + + // Set the rest! + vm_segment_set(dest, doff + off56, v56); + vm_segment_set(dest, doff + i, v00); + } + + // Finally, we always return 256 since that's all we will be able to + // write from the given block (the validation of which is done by + // checking prologue/epilogue bytes first in this function). return 256; }