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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 9837 | turbocat | 1 | /* |
| 2 | * Looks up a vertical scroll value and sets some related variables. |
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| 3 | */ |
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| 4 | #undef LOOKUP_YSCROLL_REC |
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| 5 | #define LOOKUP_YSCROLL_REC(rec_no) \ |
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| 6 | do { \ |
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| 7 | yscroll_amount = get_word(vsram + rec_no * 2) & 0x7ff; \ |
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| 8 | \ |
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| 9 | /* interlace ? */ \ |
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| 10 | if (reg[12] & 2) \ |
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| 11 | yscroll_amount >>= 1; \ |
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| 12 | \ |
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| 13 | /* Offset for the line */ \ |
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| 14 | yscroll_amount += line; \ |
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| 15 | \ |
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| 16 | yoff = ((yscroll_amount >> 3) & (ysize - 1)); \ |
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| 17 | tile_line = (tiles + ((xsize * yoff) & 0x1fff)); \ |
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| 18 | scan = (yscroll_amount & 7); \ |
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| 19 | } \ |
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| 20 | while (0) |
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| 21 | |||
| 22 | { |
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| 23 | int xsize, ysize; |
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| 24 | int x, scan = 0, w, xstart; |
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| 25 | static int sizes[4] = { 32, 64, 64, 128 }; |
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| 26 | unsigned which; |
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| 27 | unsigned char *where, *hscroll_rec_ptr, *tiles, *tile_line = NULL; |
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| 28 | int xoff, yoff, xoff_mask; |
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| 29 | int hscroll_amount, yscroll_amount = 0; |
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| 30 | uint8_t two_cell_vscroll = 0; |
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| 31 | |||
| 32 | /* |
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| 33 | * when VSCR bit is set in register 11, this is 'per 2-cell' |
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| 34 | * vertical scrolling as opposed to full screen vscrolling. |
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| 35 | */ |
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| 36 | two_cell_vscroll = ((reg[11] >> 2) & 0x1); |
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| 37 | |||
| 38 | #if PLANE == 0 |
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| 39 | // Plane 0 is only where the window isn't |
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| 40 | // This should make Herzog Zwei split screen work perfectly, and clean |
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| 41 | // up those little glitches on Sonic 3's level select. |
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| 42 | if (reg[18] & 0x80) { |
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| 43 | // Window goes down, plane 0 goes up! :) |
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| 44 | if ((line >> 3) >= (reg[18] & 0x1f)) |
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| 45 | return; |
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| 46 | } |
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| 47 | else { |
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| 48 | // Window goes up, plane 0 goes down |
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| 49 | if ((line >> 3) < (reg[18] & 0x1f)) |
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| 50 | return; |
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| 51 | } |
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| 52 | #endif |
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| 53 | |||
| 54 | /* |
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| 55 | * Get the vertical/horizontal scroll plane sizes |
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| 56 | * |
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| 57 | * 0b00: 32 cell |
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| 58 | * 0b01: 64 cell |
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| 59 | * 0b10: prohibited, but unlicensed games use this |
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| 60 | * turns out to be 64. |
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| 61 | * 0b11: 128 cell |
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| 62 | */ |
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| 63 | xsize = (sizes[(reg[16] & 3)] << 1); |
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| 64 | ysize = sizes[((reg[16] >> 4) & 3)]; |
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| 65 | |||
| 66 | /* |
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| 67 | * Here we compute pointer to the beginning of the hscroll table. |
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| 68 | * The base address of the table is stored in reg[13] << 10. |
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| 69 | */ |
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| 70 | #if PLANE == 0 |
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| 71 | hscroll_rec_ptr = (vram + ((reg[13] << 10) & 0xfc00)); |
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| 72 | tiles = (vram + (reg[2] << 10)); |
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| 73 | #else // PLANE == 1 |
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| 74 | hscroll_rec_ptr = (vram + ((reg[13] << 10) & 0xfc00) + 2); |
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| 75 | tiles = (vram + (reg[4] << 13)); |
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| 76 | #endif |
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| 77 | |||
| 78 | // Wide or narrow? |
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| 79 | if (reg[12] & 1) { |
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| 80 | w = 40; |
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| 81 | xstart = -8; |
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| 82 | } |
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| 83 | else { |
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| 84 | w = 32; |
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| 85 | xstart = 24; |
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| 86 | } |
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| 87 | |||
| 88 | /* |
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| 89 | * Lookup the horizontal offset. |
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| 90 | * See Charles MacDonald's genvdp.txt for explanation. |
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| 91 | */ |
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| 92 | switch (reg[11] & 3) { |
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| 93 | case 0: |
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| 94 | // full screen |
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| 95 | // NOP - pointer in the right place |
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| 96 | break; |
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| 97 | case 1: |
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| 98 | // invalid, but populous uses it |
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| 99 | hscroll_rec_ptr += ((line & 7) << 2); |
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| 100 | break; |
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| 101 | case 2: |
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| 102 | // per tile |
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| 103 | hscroll_rec_ptr += ((line & ~7) << 2); |
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| 104 | break; |
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| 105 | case 3: |
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| 106 | // per line |
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| 107 | hscroll_rec_ptr += (line << 2); |
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| 108 | break; |
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| 109 | } |
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| 110 | |||
| 111 | hscroll_amount = get_word(hscroll_rec_ptr); |
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| 112 | xoff_mask = xsize - 1; |
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| 113 | xoff = ((-(hscroll_amount>>3) - 1)<<1) & xoff_mask; |
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| 114 | where = dest + (xstart + (hscroll_amount & 7)) * (int) Bpp; |
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| 115 | |||
| 116 | /* |
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| 117 | * If this is not column vscroll mode, we look up the |
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| 118 | * whole screen vertical scroll value once and once only. |
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| 119 | */ |
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| 120 | if (two_cell_vscroll == 0) |
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| 121 | LOOKUP_YSCROLL_REC(PLANE); |
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| 122 | |||
| 123 | /* |
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| 124 | * Loop cells, we draw 2 more cells than expected (-1 and w) because |
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| 125 | * previously off-screen cells can be horizontally scrolled on-screen. |
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| 126 | */ |
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| 127 | for (x = -1; (x <= w); x++) { |
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| 128 | /* |
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| 129 | * If we are in 2-cell vscroll mode then lookup the amount by |
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| 130 | * which we should scroll this tile. |
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| 131 | * |
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| 132 | * If we are not in 2-cell vscroll then we looked up the value |
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| 133 | * for the whole screen vscroll earlier. |
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| 134 | * |
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| 135 | * We lookup vscroll values on even x values and this is the |
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| 136 | * vscroll value for the next two cells. Note that cell -1 is |
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| 137 | * a special case as we never looked up the vscroll value for |
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| 138 | * cell -2. |
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| 139 | */ |
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| 140 | if ((two_cell_vscroll) && ((x % 2 == 0) || (x == -1))) { |
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| 141 | |||
| 142 | /* |
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| 143 | * Note that the underflow and overflow of the table |
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| 144 | * for cell -1 and cell w is intentional. |
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| 145 | * |
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| 146 | * http://gendev.spritesmind.net/forum/viewtopic.php?t=737&postdays=0&postorder=asc&start=30 |
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| 147 | */ |
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| 148 | uint8_t cell_index = (uint8_t) x % w; |
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| 149 | int vscroll_rec_no = 2 * (cell_index / 2); |
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| 150 | |||
| 151 | /* |
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| 152 | * The records alternate, PLANE A, PLANE B, PLANE A, |
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| 153 | * ... |
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| 154 | */ |
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| 155 | #if PLANE == 1 |
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| 156 | vscroll_rec_no++; |
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| 157 | #endif |
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| 158 | LOOKUP_YSCROLL_REC(vscroll_rec_no); |
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| 159 | } |
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| 160 | |||
| 161 | #if PLANE == 0 |
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| 162 | if (reg[17] & 0x80) { |
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| 163 | // Don't draw where the window will be |
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| 164 | if (x >= ((reg[17] & 0x1f) << 1)) |
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| 165 | goto skip; |
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| 166 | } |
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| 167 | else { |
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| 168 | // + 1 so scroll layers in Sonic look right |
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| 169 | if ((x + 1) < ((reg[17] & 0x1f) << 1)) |
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| 170 | goto skip; |
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| 171 | } |
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| 172 | #endif |
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| 173 | which = get_word(tile_line + xoff); |
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| 174 | |||
| 175 | #if (FRONT == 0) && (PLANE == 1) |
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| 176 | draw_tile_solid(which, scan, where); |
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| 177 | #elif FRONT == 1 |
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| 178 | if (which >> 15) |
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| 179 | draw_tile(which, scan, where); |
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| 180 | #else |
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| 181 | if (!(which >> 15)) |
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| 182 | draw_tile(which, scan, where); |
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| 183 | #endif |
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| 184 | |||
| 185 | #if PLANE == 0 |
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| 186 | skip: |
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| 187 | #endif |
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| 188 | where += Bpp_times8; |
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| 189 | xoff = ((xoff + 2) & xoff_mask); |
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| 190 | } |
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| 191 | } |