/* * FFv1 codec * * Copyright (c) 2024 Lynne <dev@lynne.ee> * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ struct RangeCoder {    uint64_t bytestream_start;    uint64_t bytestream;    uint64_t bytestream_end;     int low;    int range;    uint16_t outstanding_count;    uint8_t outstanding_byte;}; /* Full renorm version that can handle outstanding_byte == 0xFF */void renorm_encoder_full(inout RangeCoder c){    int bs_cnt = 0;    u8buf bytestream = u8buf(c.bytestream);     if (c.outstanding_byte == 0xFF) {        c.outstanding_byte = uint8_t(c.low >> 8);    } else if (c.low <= 0xFF00) {        bytestream[bs_cnt++].v = c.outstanding_byte;        uint16_t cnt = c.outstanding_count;        for (; cnt > 0; cnt--)            bytestream[bs_cnt++].v = uint8_t(0xFF);        c.outstanding_count = uint16_t(0);        c.outstanding_byte = uint8_t(c.low >> 8);    } else if (c.low >= 0x10000) {        bytestream[bs_cnt++].v = c.outstanding_byte + uint8_t(1);        uint16_t cnt = c.outstanding_count;        for (; cnt > 0; cnt--)            bytestream[bs_cnt++].v = uint8_t(0x00);        c.outstanding_count = uint16_t(0);        c.outstanding_byte = uint8_t(bitfieldExtract(c.low, 8, 8));    } else {        c.outstanding_count++;    }     c.bytestream += bs_cnt;    c.range <<= 8;    c.low = bitfieldInsert(0, c.low, 8, 8);} /* Cannot deal with outstanding_byte == -1 in the name of speed */void renorm_encoder(inout RangeCoder c){    uint16_t oc = c.outstanding_count + uint16_t(1);    int low = c.low;     c.range <<= 8;    c.low = bitfieldInsert(0, low, 8, 8);     if (low > 0xFF00 && low < 0x10000) {        c.outstanding_count = oc;        return;    }     u8buf bs = u8buf(c.bytestream);    uint8_t outstanding_byte = c.outstanding_byte;     c.bytestream        = uint64_t(bs) + oc;    c.outstanding_count = uint16_t(0);    c.outstanding_byte  = uint8_t(low >> 8);     uint8_t obs = uint8_t(low > 0xFF00);    uint8_t fill = obs - uint8_t(1); /* unsigned underflow */     bs[0].v = outstanding_byte + obs;    for (int i = 1; i < oc; i++)        bs[i].v = fill;} void put_rac_norenorm(inout RangeCoder c, uint64_t state, bool bit){    u8buf sb = u8buf(state);    uint val = uint(sb.v);    int range1 = uint16_t((c.range * val) >> 8); #ifdef DEBUG    if (val == 0)        debugPrintfEXT("Error: state is zero (addr: 0x%lx)", uint64_t(sb));    if (range1 >= c.range)        debugPrintfEXT("Error: range1 >= c.range");    if (range1 <= 0)        debugPrintfEXT("Error: range1 <= 0");#endif     int diff = c.range - range1;    if (bit) {        c.low   += diff;        c.range  = range1;    } else {        c.range  = diff;    }     sb.v = zero_one_state[(uint(bit) << 8) + val]; #ifdef DEBUG    if (sb.v == 0)        debugPrintfEXT("Error: inserted zero state from tab %i idx %i", bit, val);#endif} /* Equiprobable bit */void put_rac_equi(inout RangeCoder c, bool bit){    int range1 = c.range >> 1; #ifdef DEBUG    if (range1 >= c.range)        debugPrintfEXT("Error: range1 >= c.range");    if (range1 <= 0)        debugPrintfEXT("Error: range1 <= 0");#endif     if (bit) {        c.low   += c.range - range1;        c.range  = range1;    } else {        c.range -= range1;    }     if (expectEXT(c.range < 0x100, false))        renorm_encoder(c);} void put_rac_terminate(inout RangeCoder c){    int range1 = (c.range * 129) >> 8; #ifdef DEBUG    if (range1 >= c.range)        debugPrintfEXT("Error: range1 >= c.range");    if (range1 <= 0)        debugPrintfEXT("Error: range1 <= 0");#endif     c.range -= range1;    if (expectEXT(c.range < 0x100, false))        renorm_encoder(c);} /* Return the number of bytes written. */uint32_t rac_terminate(inout RangeCoder c){    put_rac_terminate(c);    c.range = uint16_t(0xFF);    c.low  += 0xFF;    renorm_encoder(c);    c.range = uint16_t(0xFF);    renorm_encoder(c); #ifdef DEBUG    if (c.low != 0)        debugPrintfEXT("Error: c.low != 0");    if (c.range < 0x100)        debugPrintfEXT("Error: range < 0x100");#endif     return uint32_t(uint64_t(c.bytestream) - uint64_t(c.bytestream_start));} void rac_init(out RangeCoder r, u8buf data, uint buf_size){    r.bytestream_start = uint64_t(data);    r.bytestream = uint64_t(data);    r.bytestream_end = uint64_t(data) + buf_size;    r.low = 0;    r.range = 0xFF00;    r.outstanding_count = uint16_t(0);    r.outstanding_byte = uint8_t(0xFF);} /* Decoder */uint overread = 0;bool corrupt = false; void rac_init_dec(out RangeCoder r, u8buf data, uint buf_size){    overread = 0;    corrupt = false;     /* Skip priming bytes */    rac_init(r, OFFBUF(u8buf, data, 2), buf_size - 2);     u8vec2 prime = u8vec2buf(data).v;    /* Switch endianess of the priming bytes */    r.low = pack16(prime.yx);     if (r.low >= 0xFF00) {        r.low = 0xFF00;        r.bytestream_end = uint64_t(data) + 2;    }} void refill(inout RangeCoder c){    c.range <<= 8;    c.low   <<= 8;    if (expectEXT(c.bytestream < c.bytestream_end, false)) {        c.low |= u8buf(c.bytestream).v;        c.bytestream++;    } else {        overread++;    }} bool get_rac_direct(inout RangeCoder c, inout uint8_t state){    int range1 = c.range * state >> 8;    int ranged = c.range - range1;     bool bit = c.low >= ranged;    c.low -= bit ? ranged : 0;    c.range = (bit ? 0 : ranged) + (bit ? range1 : 0);     if (expectEXT(c.range < 0x100, false))        refill(c);     state = zero_one_state[state + (bit ? 256 : 0)];    return bit;} bool get_rac(inout RangeCoder c, uint64_t state){    return get_rac_direct(c, u8buf(state).v);} bool get_rac_equi(inout RangeCoder c){    int range1 = c.range >> 1;     c.range -= range1;     bool bit = c.low >= c.range;    if (bit) {        c.low -= c.range;        c.range = range1;    }     if (expectEXT(c.range < 0x100, false))        refill(c);     return bit;}