/* inffast.c -- fast decoding * Copyright (C) 1995-2003 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"#ifndef ASMINF/* Allow machine dependent optimization for post-increment or pre-increment.   Based on testing to date,   Pre-increment preferred for:   - PowerPC G3 (Adler)   - MIPS R5000 (Randers-Pehrson)   Post-increment preferred for:   - none   No measurable difference:   - Pentium III (Anderson)   - 68060 (Nikl) */#ifdef POSTINC#  define OFF 0#  define PUP(a) *(a)++#else#  define OFF 1#  define PUP(a) *++(a)#endif/*   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 inflate_fast(strm, start)z_streamp strm;unsigned start;         /* inflate()'s starting value for strm->avail_out */{    struct inflate_state FAR *state;    unsigned char FAR *in;      /* local strm->next_in */    unsigned char FAR *last;    /* while in < last, enough input available */    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 */    unsigned wsize;             /* window size or zero if not using window */    unsigned whave;             /* valid bytes in the window */    unsigned write;             /* 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 this;                  /* 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 - OFF;    last = in + (strm->avail_in - 5);    out = strm->next_out - OFF;    beg = out - (start - strm->avail_out);    end = out + (strm->avail_out - 257);    wsize = state->wsize;    whave = state->whave;    write = state->write;    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)(PUP(in)) << bits;            bits += 8;            hold += (unsigned long)(PUP(in)) << bits;            bits += 8;        }        this = lcode[hold & lmask];      dolen:        op = (unsigned)(this.bits);        hold >>= op;        bits -= op;        op = (unsigned)(this.op);        if (op == 0) {                          /* literal */            Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?                    "inflate:         literal '%c'\n" :                    "inflate:         literal 0x%02x\n", this.val));            PUP(out) = (unsigned char)(this.val);        }        else if (op & 16) {                     /* length base */            len = (unsigned)(this.val);            op &= 15;                           /* number of extra bits */            if (op) {                if (bits < op) {                    hold += (unsigned long)(PUP(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)(PUP(in)) << bits;                bits += 8;                hold += (unsigned long)(PUP(in)) << bits;                bits += 8;            }            this = dcode[hold & dmask];          dodist:            op = (unsigned)(this.bits);            hold >>= op;            bits -= op;            op = (unsigned)(this.op);            if (op & 16) {                      /* distance base */                dist = (unsigned)(this.val);                op &= 15;                       /* number of extra bits */                if (bits < op) {                    hold += (unsigned long)(PUP(in)) << bits;                    bits += 8;                    if (bits < op) {                        hold += (unsigned long)(PUP(in)) << bits;                        bits += 8;                    }                }                dist += (unsigned)hold & ((1U << op) - 1);                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) {                        strm->msg = (char *)"invalid distance too far back";                        state->mode = BAD;                        break;                    }                    from = window - OFF;                    if (write == 0) {           /* very common case */                        from += wsize - op;                        if (op < len) {         /* some from window */                            len -= op;                            do {                                PUP(out) = PUP(from);                            } while (--op);                            from = out - dist;  /* rest from output */                        }                    }                    else if (write < op) {      /* wrap around window */                        from += wsize + write - op;                        op -= write;                        if (op < len) {         /* some from end of window */                            len -= op;                            do {                                PUP(out) = PUP(from);                            } while (--op);                            from = window - OFF;                            if (write < len) {  /* some from start of window */                                op = write;                                len -= op;                                do {                                    PUP(out) = PUP(from);                                } while (--op);                                from = out - dist;      /* rest from output */                            }                        }                    }                    else {                      /* contiguous in window */                        from += write - op;                        if (op < len) {         /* some from window */                            len -= op;                            do {                                PUP(out) = PUP(from);                            } while (--op);                            from = out - dist;  /* rest from output */                        }                    }                    while (len > 2) {                        PUP(out) = PUP(from);                        PUP(out) = PUP(from);                        PUP(out) = PUP(from);                        len -= 3;                    }                    if (len) {                        PUP(out) = PUP(from);                        if (len > 1)                            PUP(out) = PUP(from);                    }                }                else {                    from = out - dist;          /* copy direct from output */                    do {                        /* minimum length is three */                        PUP(out) = PUP(from);                        PUP(out) = PUP(from);                        PUP(out) = PUP(from);                        len -= 3;                    } while (len > 2);                    if (len) {                        PUP(out) = PUP(from);                        if (len > 1)                            PUP(out) = PUP(from);                    }                }            }            else if ((op & 64) == 0) {          /* 2nd level distance code */                this = dcode[this.val + (hold & ((1U << op) - 1))];                goto dodist;            }            else {                strm->msg = (char *)"invalid distance code";                state->mode = BAD;                break;            }        }        else if ((op & 64) == 0) {              /* 2nd level length code */            this = lcode[this.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 = (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 + OFF;    strm->next_out = out + OFF;    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 write == 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 */