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https://github.com/joncampbell123/dosbox-x.git
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43 lines
2.2 KiB
C
43 lines
2.2 KiB
C
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/* mapping function from 16-bit WORD to font RAM offset */
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/* in: code = 16-bit JIS code word (unshifted)
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* line = scan line within character cell
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* right_half = 1 if right half, 0 if left half (double-wide only)
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* out: byte offset in FONT RAM (0x00000-0x7FFFF inclusive)
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*
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* NTS: Font ROM/RAM in PC-98 is laid out as follows in this emulation:
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*
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* 0x00 0xAA ASCII single-wide character AA offset = (AA * 16)
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* 0xHH 0xLL Double-wide char (HH != 0) number HHLL offset = ((HH & 0x7F) * 256) + ((LL & 0x7F) * 2) + right_half
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*
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* Visual layout:
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*
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+................
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* | | | | | | | | | | | | | | | | |................ 0x00 to 0xFF, 8-bit wide, at 0x0000
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+................
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* | | | | | | | | |................ 0x0100 to 0x7F7F, 16-bit wide, at 0x0100, lower 7 bits only each byte
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* +---+---+---+---+---+---+---+---+................
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*
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* This is not necessarily how the font data is stored in ROM on actual hardware.
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* The hardware appears to accept 16 bits but only use the low 7 bits of each byte for double-wide.
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* 0x80 0xAA is NOT an alias of single-wide chars. */
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static inline uint32_t pc98_font_char_to_ofs(const uint16_t code,const uint8_t line,const uint8_t right_half) {
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if (code & 0xFF00) {
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/* double-wide. this maps 0x01-0x7F, 0x80 to 0x80, 0x81-0xFF to 0x01-0x7F */
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const uint16_t x_code = (code & 0x7F) + ((((code + 0x7F00) & 0x7F00) + 0x0100) >> 1); /* 16-bit to 14-bit conversion. */
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return ((((uint32_t)x_code * (uint32_t)16) + (uint32_t)(line & 0xF)) * (uint32_t)2) + (uint32_t)right_half;
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}
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else {
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/* single-wide */
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return ((uint32_t)code * (uint32_t)16) + (line & 0xF);
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}
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}
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static inline uint8_t pc98_font_char_read(const uint16_t code,const uint8_t line,const uint8_t right_half) {
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return vga.draw.font[pc98_font_char_to_ofs(code,line,right_half)];
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}
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static inline void pc98_font_char_write(const uint16_t code,const uint8_t line,const uint8_t right_half,const uint8_t byte) {
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vga.draw.font[pc98_font_char_to_ofs(code,line,right_half)] = byte;
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}
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