/* inffast.c -- fast decoding

 * Copyright (C) 1995-2026 Mark Adler

 * For conditions of distribution and use, see copyright notice in zlib.h

 */

#include "zutil.h"

#include "inftrees.h"

#include "inflate.h"

#include "inffast.h"

#ifdef ASMINF

#  pragma message("Assembler code may have bugs -- use at your own risk")

#else

/*

   Decode literal, length, and distance codes and write out the resulting

   literal and match bytes until either not enough input or output is

   available, an end-of-block is encountered, or a data error is encountered.

   When large enough input and output buffers are supplied to inflate(), for

   example, a 16K input buffer and a 64K output buffer, more than 95% of the

   inflate execution time is spent in this routine.

   Entry assumptions:

        state->mode == LEN

        strm->avail_in >= 6

        strm->avail_out >= 258

        start >= strm->avail_out

        state->bits < 8

   On return, state->mode is one of:

        LEN -- ran out of enough output space or enough available input

        TYPE -- reached end of block code, inflate() to interpret next block

        BAD -- error in block data

   Notes:

    - The maximum input bits used by a length/distance pair is 15 bits for the

      length code, 5 bits for the length extra, 15 bits for the distance code,

      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.

      Therefore if strm->avail_in >= 6, then there is enough input to avoid

      checking for available input while decoding.

    - The maximum bytes that a single length/distance pair can output is 258

      bytes, which is the maximum length that can be coded.  inflate_fast()

      requires strm->avail_out >= 258 for each loop to avoid checking for

      output space.

 */

void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {

    struct inflate_state FAR *state;

    z_const unsigned char FAR *in;      /* local strm->next_in */

    z_const unsigned char FAR *last;    /* have enough input while in < last */

    unsigned char FAR *out;     /* local strm->next_out */

    unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */

    unsigned char FAR *end;     /* while out < end, enough space available */

#ifdef INFLATE_STRICT

    unsigned dmax;              /* maximum distance from zlib header */

#endif

    unsigned wsize;             /* window size or zero if not using window */

    unsigned whave;             /* valid bytes in the window */

    unsigned wnext;             /* window write index */

    unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */

    unsigned long hold;         /* local strm->hold */

    unsigned bits;              /* local strm->bits */

    code const FAR *lcode;      /* local strm->lencode */

    code const FAR *dcode;      /* local strm->distcode */

    unsigned lmask;             /* mask for first level of length codes */

    unsigned dmask;             /* mask for first level of distance codes */

    code const *here;           /* retrieved table entry */

    unsigned op;                /* code bits, operation, extra bits, or */

                                /*  window position, window bytes to copy */

    unsigned len;               /* match length, unused bytes */

    unsigned dist;              /* match distance */

    unsigned char FAR *from;    /* where to copy match from */

    /* copy state to local variables */

    state = (struct inflate_state FAR *)strm->state;

    in = strm->next_in;

    last = in + (strm->avail_in - 5);

    out = strm->next_out;

    beg = out - (start - strm->avail_out);

    end = out + (strm->avail_out - 257);

#ifdef INFLATE_STRICT

    dmax = state->dmax;

#endif

    wsize = state->wsize;

    whave = state->whave;

    wnext = state->wnext;

    window = state->window;

    hold = state->hold;

    bits = state->bits;

    lcode = state->lencode;

    dcode = state->distcode;

    lmask = (1U << state->lenbits) - 1;

    dmask = (1U << state->distbits) - 1;

    /* decode literals and length/distances until end-of-block or not enough

       input data or output space */

    do {

        if (bits < 15) {

            hold += (unsigned long)(*in++) << bits;

            bits += 8;

            hold += (unsigned long)(*in++) << bits;

            bits += 8;

        }

        here = lcode + (hold & lmask);

      dolen:

        op = (unsigned)(here->bits);

        hold >>= op;

        bits -= op;

        op = (unsigned)(here->op);

        if (op == 0) {                          /* literal */

            Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?

                    "inflate:         literal '%c'\n" :

                    "inflate:         literal 0x%02x\n", here->val));

            *out++ = (unsigned char)(here->val);

        }

        else if (op & 16) {                     /* length base */

            len = (unsigned)(here->val);

            op &= 15;                           /* number of extra bits */

            if (op) {

                if (bits < op) {

                    hold += (unsigned long)(*in++) << bits;

                    bits += 8;

                }

                len += (unsigned)hold & ((1U << op) - 1);

                hold >>= op;

                bits -= op;

            }

            Tracevv((stderr, "inflate:         length %u\n", len));

            if (bits < 15) {

                hold += (unsigned long)(*in++) << bits;

                bits += 8;

                hold += (unsigned long)(*in++) << bits;

                bits += 8;

            }

            here = dcode + (hold & dmask);

          dodist:

            op = (unsigned)(here->bits);

            hold >>= op;

            bits -= op;

            op = (unsigned)(here->op);

            if (op & 16) {                      /* distance base */

                dist = (unsigned)(here->val);

                op &= 15;                       /* number of extra bits */

                if (bits < op) {

                    hold += (unsigned long)(*in++) << bits;

                    bits += 8;

                    if (bits < op) {

                        hold += (unsigned long)(*in++) << bits;

                        bits += 8;

                    }

                }

                dist += (unsigned)hold & ((1U << op) - 1);

#ifdef INFLATE_STRICT

                if (dist > dmax) {

                    strm->msg = (z_const char *)

                        "invalid distance too far back";

                    state->mode = BAD;

                    break;

                }

#endif

                hold >>= op;

                bits -= op;

                Tracevv((stderr, "inflate:         distance %u\n", dist));

                op = (unsigned)(out - beg);     /* max distance in output */

                if (dist > op) {                /* see if copy from window */

                    op = dist - op;             /* distance back in window */

                    if (op > whave) {

                        if (state->sane) {

                            strm->msg = (z_const char *)

                                "invalid distance too far back";

                            state->mode = BAD;

                            break;

                        }

#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR

                        if (len <= op - whave) {

                            do {

                                *out++ = 0;

                            } while (--len);

                            continue;

                        }

                        len -= op - whave;

                        do {

                            *out++ = 0;

                        } while (--op > whave);

                        if (op == 0) {

                            from = out - dist;

                            do {

                                *out++ = *from++;

                            } while (--len);

                            continue;

                        }

#endif

                    }

                    from = window;

                    if (wnext == 0) {           /* very common case */

                        from += wsize - op;

                        if (op < len) {         /* some from window */

                            len -= op;

                            do {

                                *out++ = *from++;

                            } while (--op);

                            from = out - dist;  /* rest from output */

                        }

                    }

                    else if (wnext < op) {      /* wrap around window */

                        from += wsize + wnext - op;

                        op -= wnext;

                        if (op < len) {         /* some from end of window */

                            len -= op;

                            do {

                                *out++ = *from++;

                            } while (--op);

                            from = window;

                            if (wnext < len) {  /* some from start of window */

                                op = wnext;

                                len -= op;

                                do {

                                    *out++ = *from++;

                                } while (--op);

                                from = out - dist;      /* rest from output */

                            }

                        }

                    }

                    else {                      /* contiguous in window */

                        from += wnext - op;

                        if (op < len) {         /* some from window */

                            len -= op;

                            do {

                                *out++ = *from++;

                            } while (--op);

                            from = out - dist;  /* rest from output */

                        }

                    }

                    while (len > 2) {

                        *out++ = *from++;

                        *out++ = *from++;

                        *out++ = *from++;

                        len -= 3;

                    }

                    if (len) {

                        *out++ = *from++;

                        if (len > 1)

                            *out++ = *from++;

                    }

                }

                else {

                    from = out - dist;          /* copy direct from output */

                    do {                        /* minimum length is three */

                        *out++ = *from++;

                        *out++ = *from++;

                        *out++ = *from++;

                        len -= 3;

                    } while (len > 2);

                    if (len) {

                        *out++ = *from++;

                        if (len > 1)

                            *out++ = *from++;

                    }

                }

            }

            else if ((op & 64) == 0) {          /* 2nd level distance code */

                here = dcode + here->val + (hold & ((1U << op) - 1));

                goto dodist;

            }

            else {

                strm->msg = (z_const char *)"invalid distance code";

                state->mode = BAD;

                break;

            }

        }

        else if ((op & 64) == 0) {              /* 2nd level length code */

            here = lcode + here->val + (hold & ((1U << op) - 1));

            goto dolen;

        }

        else if (op & 32) {                     /* end-of-block */

            Tracevv((stderr, "inflate:         end of block\n"));

            state->mode = TYPE;

            break;

        }

        else {

            strm->msg = (z_const char *)"invalid literal/length code";

            state->mode = BAD;

            break;

        }

    } while (in < last && out < end);

    /* return unused bytes (on entry, bits < 8, so in won't go too far back) */

    len = bits >> 3;

    in -= len;

    bits -= len << 3;

    hold &= (1U << bits) - 1;

    /* update state and return */

    strm->next_in = in;

    strm->next_out = out;

    strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));

    strm->avail_out = (unsigned)(out < end ?

                                 257 + (end - out) : 257 - (out - end));

    state->hold = hold;

    state->bits = bits;

    return;

}

/*

   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):

   - Using bit fields for code structure

   - Different op definition to avoid & for extra bits (do & for table bits)

   - Three separate decoding do-loops for direct, window, and wnext == 0

   - Special case for distance > 1 copies to do overlapped load and store copy

   - Explicit branch predictions (based on measured branch probabilities)

   - Deferring match copy and interspersed it with decoding subsequent codes

   - Swapping literal/length else

   - Swapping window/direct else

   - Larger unrolled copy loops (three is about right)

   - Moving len -= 3 statement into middle of loop

 */

#endif /* !ASMINF */