michael@0: /* gzlib.c -- zlib functions common to reading and writing gzip files
michael@0:  * Copyright (C) 2004, 2010, 2011, 2012, 2013 Mark Adler
michael@0:  * For conditions of distribution and use, see copyright notice in zlib.h
michael@0:  */
michael@0: 
michael@0: #include "gzguts.h"
michael@0: 
michael@0: #if defined(_WIN32) && !defined(__BORLANDC__)
michael@0: #  define LSEEK _lseeki64
michael@0: #else
michael@0: #if defined(_LARGEFILE64_SOURCE) && _LFS64_LARGEFILE-0
michael@0: #  define LSEEK lseek64
michael@0: #else
michael@0: #  define LSEEK lseek
michael@0: #endif
michael@0: #endif
michael@0: 
michael@0: /* Local functions */
michael@0: local void gz_reset OF((gz_statep));
michael@0: local gzFile gz_open OF((const void *, int, const char *));
michael@0: 
michael@0: #if defined UNDER_CE
michael@0: 
michael@0: /* Map the Windows error number in ERROR to a locale-dependent error message
michael@0:    string and return a pointer to it.  Typically, the values for ERROR come
michael@0:    from GetLastError.
michael@0: 
michael@0:    The string pointed to shall not be modified by the application, but may be
michael@0:    overwritten by a subsequent call to gz_strwinerror
michael@0: 
michael@0:    The gz_strwinerror function does not change the current setting of
michael@0:    GetLastError. */
michael@0: char ZLIB_INTERNAL *gz_strwinerror (error)
michael@0:      DWORD error;
michael@0: {
michael@0:     static char buf[1024];
michael@0: 
michael@0:     wchar_t *msgbuf;
michael@0:     DWORD lasterr = GetLastError();
michael@0:     DWORD chars = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
michael@0:         | FORMAT_MESSAGE_ALLOCATE_BUFFER,
michael@0:         NULL,
michael@0:         error,
michael@0:         0, /* Default language */
michael@0:         (LPVOID)&msgbuf,
michael@0:         0,
michael@0:         NULL);
michael@0:     if (chars != 0) {
michael@0:         /* If there is an \r\n appended, zap it.  */
michael@0:         if (chars >= 2
michael@0:             && msgbuf[chars - 2] == '\r' && msgbuf[chars - 1] == '\n') {
michael@0:             chars -= 2;
michael@0:             msgbuf[chars] = 0;
michael@0:         }
michael@0: 
michael@0:         if (chars > sizeof (buf) - 1) {
michael@0:             chars = sizeof (buf) - 1;
michael@0:             msgbuf[chars] = 0;
michael@0:         }
michael@0: 
michael@0:         wcstombs(buf, msgbuf, chars + 1);
michael@0:         LocalFree(msgbuf);
michael@0:     }
michael@0:     else {
michael@0:         sprintf(buf, "unknown win32 error (%ld)", error);
michael@0:     }
michael@0: 
michael@0:     SetLastError(lasterr);
michael@0:     return buf;
michael@0: }
michael@0: 
michael@0: #endif /* UNDER_CE */
michael@0: 
michael@0: /* Reset gzip file state */
michael@0: local void gz_reset(state)
michael@0:     gz_statep state;
michael@0: {
michael@0:     state->x.have = 0;              /* no output data available */
michael@0:     if (state->mode == GZ_READ) {   /* for reading ... */
michael@0:         state->eof = 0;             /* not at end of file */
michael@0:         state->past = 0;            /* have not read past end yet */
michael@0:         state->how = LOOK;          /* look for gzip header */
michael@0:     }
michael@0:     state->seek = 0;                /* no seek request pending */
michael@0:     gz_error(state, Z_OK, NULL);    /* clear error */
michael@0:     state->x.pos = 0;               /* no uncompressed data yet */
michael@0:     state->strm.avail_in = 0;       /* no input data yet */
michael@0: }
michael@0: 
michael@0: /* Open a gzip file either by name or file descriptor. */
michael@0: local gzFile gz_open(path, fd, mode)
michael@0:     const void *path;
michael@0:     int fd;
michael@0:     const char *mode;
michael@0: {
michael@0:     gz_statep state;
michael@0:     size_t len;
michael@0:     int oflag;
michael@0: #ifdef O_CLOEXEC
michael@0:     int cloexec = 0;
michael@0: #endif
michael@0: #ifdef O_EXCL
michael@0:     int exclusive = 0;
michael@0: #endif
michael@0: 
michael@0:     /* check input */
michael@0:     if (path == NULL)
michael@0:         return NULL;
michael@0: 
michael@0:     /* allocate gzFile structure to return */
michael@0:     state = (gz_statep)malloc(sizeof(gz_state));
michael@0:     if (state == NULL)
michael@0:         return NULL;
michael@0:     state->size = 0;            /* no buffers allocated yet */
michael@0:     state->want = GZBUFSIZE;    /* requested buffer size */
michael@0:     state->msg = NULL;          /* no error message yet */
michael@0: 
michael@0:     /* interpret mode */
michael@0:     state->mode = GZ_NONE;
michael@0:     state->level = Z_DEFAULT_COMPRESSION;
michael@0:     state->strategy = Z_DEFAULT_STRATEGY;
michael@0:     state->direct = 0;
michael@0:     while (*mode) {
michael@0:         if (*mode >= '0' && *mode <= '9')
michael@0:             state->level = *mode - '0';
michael@0:         else
michael@0:             switch (*mode) {
michael@0:             case 'r':
michael@0:                 state->mode = GZ_READ;
michael@0:                 break;
michael@0: #ifndef NO_GZCOMPRESS
michael@0:             case 'w':
michael@0:                 state->mode = GZ_WRITE;
michael@0:                 break;
michael@0:             case 'a':
michael@0:                 state->mode = GZ_APPEND;
michael@0:                 break;
michael@0: #endif
michael@0:             case '+':       /* can't read and write at the same time */
michael@0:                 free(state);
michael@0:                 return NULL;
michael@0:             case 'b':       /* ignore -- will request binary anyway */
michael@0:                 break;
michael@0: #ifdef O_CLOEXEC
michael@0:             case 'e':
michael@0:                 cloexec = 1;
michael@0:                 break;
michael@0: #endif
michael@0: #ifdef O_EXCL
michael@0:             case 'x':
michael@0:                 exclusive = 1;
michael@0:                 break;
michael@0: #endif
michael@0:             case 'f':
michael@0:                 state->strategy = Z_FILTERED;
michael@0:                 break;
michael@0:             case 'h':
michael@0:                 state->strategy = Z_HUFFMAN_ONLY;
michael@0:                 break;
michael@0:             case 'R':
michael@0:                 state->strategy = Z_RLE;
michael@0:                 break;
michael@0:             case 'F':
michael@0:                 state->strategy = Z_FIXED;
michael@0:                 break;
michael@0:             case 'T':
michael@0:                 state->direct = 1;
michael@0:                 break;
michael@0:             default:        /* could consider as an error, but just ignore */
michael@0:                 ;
michael@0:             }
michael@0:         mode++;
michael@0:     }
michael@0: 
michael@0:     /* must provide an "r", "w", or "a" */
michael@0:     if (state->mode == GZ_NONE) {
michael@0:         free(state);
michael@0:         return NULL;
michael@0:     }
michael@0: 
michael@0:     /* can't force transparent read */
michael@0:     if (state->mode == GZ_READ) {
michael@0:         if (state->direct) {
michael@0:             free(state);
michael@0:             return NULL;
michael@0:         }
michael@0:         state->direct = 1;      /* for empty file */
michael@0:     }
michael@0: 
michael@0:     /* save the path name for error messages */
michael@0: #ifdef _WIN32
michael@0:     if (fd == -2) {
michael@0:         len = wcstombs(NULL, path, 0);
michael@0:         if (len == (size_t)-1)
michael@0:             len = 0;
michael@0:     }
michael@0:     else
michael@0: #endif
michael@0:         len = strlen((const char *)path);
michael@0:     state->path = (char *)malloc(len + 1);
michael@0:     if (state->path == NULL) {
michael@0:         free(state);
michael@0:         return NULL;
michael@0:     }
michael@0: #ifdef _WIN32
michael@0:     if (fd == -2)
michael@0:         if (len)
michael@0:             wcstombs(state->path, path, len + 1);
michael@0:         else
michael@0:             *(state->path) = 0;
michael@0:     else
michael@0: #endif
michael@0: #if !defined(NO_snprintf) && !defined(NO_vsnprintf)
michael@0:         snprintf(state->path, len + 1, "%s", (const char *)path);
michael@0: #else
michael@0:         strcpy(state->path, path);
michael@0: #endif
michael@0: 
michael@0:     /* compute the flags for open() */
michael@0:     oflag =
michael@0: #ifdef O_LARGEFILE
michael@0:         O_LARGEFILE |
michael@0: #endif
michael@0: #ifdef O_BINARY
michael@0:         O_BINARY |
michael@0: #endif
michael@0: #ifdef O_CLOEXEC
michael@0:         (cloexec ? O_CLOEXEC : 0) |
michael@0: #endif
michael@0:         (state->mode == GZ_READ ?
michael@0:          O_RDONLY :
michael@0:          (O_WRONLY | O_CREAT |
michael@0: #ifdef O_EXCL
michael@0:           (exclusive ? O_EXCL : 0) |
michael@0: #endif
michael@0:           (state->mode == GZ_WRITE ?
michael@0:            O_TRUNC :
michael@0:            O_APPEND)));
michael@0: 
michael@0:     /* open the file with the appropriate flags (or just use fd) */
michael@0:     state->fd = fd > -1 ? fd : (
michael@0: #ifdef _WIN32
michael@0:         fd == -2 ? _wopen(path, oflag, 0666) :
michael@0: #endif
michael@0:         open((const char *)path, oflag, 0666));
michael@0:     if (state->fd == -1) {
michael@0:         free(state->path);
michael@0:         free(state);
michael@0:         return NULL;
michael@0:     }
michael@0:     if (state->mode == GZ_APPEND)
michael@0:         state->mode = GZ_WRITE;         /* simplify later checks */
michael@0: 
michael@0:     /* save the current position for rewinding (only if reading) */
michael@0:     if (state->mode == GZ_READ) {
michael@0:         state->start = LSEEK(state->fd, 0, SEEK_CUR);
michael@0:         if (state->start == -1) state->start = 0;
michael@0:     }
michael@0: 
michael@0:     /* initialize stream */
michael@0:     gz_reset(state);
michael@0: 
michael@0:     /* return stream */
michael@0:     return (gzFile)state;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: gzFile ZEXPORT gzopen(path, mode)
michael@0:     const char *path;
michael@0:     const char *mode;
michael@0: {
michael@0:     return gz_open(path, -1, mode);
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: gzFile ZEXPORT gzopen64(path, mode)
michael@0:     const char *path;
michael@0:     const char *mode;
michael@0: {
michael@0:     return gz_open(path, -1, mode);
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: gzFile ZEXPORT gzdopen(fd, mode)
michael@0:     int fd;
michael@0:     const char *mode;
michael@0: {
michael@0:     char *path;         /* identifier for error messages */
michael@0:     gzFile gz;
michael@0: 
michael@0:     if (fd == -1 || (path = (char *)malloc(7 + 3 * sizeof(int))) == NULL)
michael@0:         return NULL;
michael@0: #if !defined(NO_snprintf) && !defined(NO_vsnprintf)
michael@0:     snprintf(path, 7 + 3 * sizeof(int), "<fd:%d>", fd); /* for debugging */
michael@0: #else
michael@0:     sprintf(path, "<fd:%d>", fd);   /* for debugging */
michael@0: #endif
michael@0:     gz = gz_open(path, fd, mode);
michael@0:     free(path);
michael@0:     return gz;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: #ifdef _WIN32
michael@0: gzFile ZEXPORT gzopen_w(path, mode)
michael@0:     const wchar_t *path;
michael@0:     const char *mode;
michael@0: {
michael@0:     return gz_open(path, -2, mode);
michael@0: }
michael@0: #endif
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: int ZEXPORT gzbuffer(file, size)
michael@0:     gzFile file;
michael@0:     unsigned size;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return -1;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return -1;
michael@0: 
michael@0:     /* make sure we haven't already allocated memory */
michael@0:     if (state->size != 0)
michael@0:         return -1;
michael@0: 
michael@0:     /* check and set requested size */
michael@0:     if (size < 2)
michael@0:         size = 2;               /* need two bytes to check magic header */
michael@0:     state->want = size;
michael@0:     return 0;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: int ZEXPORT gzrewind(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure */
michael@0:     if (file == NULL)
michael@0:         return -1;
michael@0:     state = (gz_statep)file;
michael@0: 
michael@0:     /* check that we're reading and that there's no error */
michael@0:     if (state->mode != GZ_READ ||
michael@0:             (state->err != Z_OK && state->err != Z_BUF_ERROR))
michael@0:         return -1;
michael@0: 
michael@0:     /* back up and start over */
michael@0:     if (LSEEK(state->fd, state->start, SEEK_SET) == -1)
michael@0:         return -1;
michael@0:     gz_reset(state);
michael@0:     return 0;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off64_t ZEXPORT gzseek64(file, offset, whence)
michael@0:     gzFile file;
michael@0:     z_off64_t offset;
michael@0:     int whence;
michael@0: {
michael@0:     unsigned n;
michael@0:     z_off64_t ret;
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return -1;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return -1;
michael@0: 
michael@0:     /* check that there's no error */
michael@0:     if (state->err != Z_OK && state->err != Z_BUF_ERROR)
michael@0:         return -1;
michael@0: 
michael@0:     /* can only seek from start or relative to current position */
michael@0:     if (whence != SEEK_SET && whence != SEEK_CUR)
michael@0:         return -1;
michael@0: 
michael@0:     /* normalize offset to a SEEK_CUR specification */
michael@0:     if (whence == SEEK_SET)
michael@0:         offset -= state->x.pos;
michael@0:     else if (state->seek)
michael@0:         offset += state->skip;
michael@0:     state->seek = 0;
michael@0: 
michael@0:     /* if within raw area while reading, just go there */
michael@0:     if (state->mode == GZ_READ && state->how == COPY &&
michael@0:             state->x.pos + offset >= 0) {
michael@0:         ret = LSEEK(state->fd, offset - state->x.have, SEEK_CUR);
michael@0:         if (ret == -1)
michael@0:             return -1;
michael@0:         state->x.have = 0;
michael@0:         state->eof = 0;
michael@0:         state->past = 0;
michael@0:         state->seek = 0;
michael@0:         gz_error(state, Z_OK, NULL);
michael@0:         state->strm.avail_in = 0;
michael@0:         state->x.pos += offset;
michael@0:         return state->x.pos;
michael@0:     }
michael@0: 
michael@0:     /* calculate skip amount, rewinding if needed for back seek when reading */
michael@0:     if (offset < 0) {
michael@0:         if (state->mode != GZ_READ)         /* writing -- can't go backwards */
michael@0:             return -1;
michael@0:         offset += state->x.pos;
michael@0:         if (offset < 0)                     /* before start of file! */
michael@0:             return -1;
michael@0:         if (gzrewind(file) == -1)           /* rewind, then skip to offset */
michael@0:             return -1;
michael@0:     }
michael@0: 
michael@0:     /* if reading, skip what's in output buffer (one less gzgetc() check) */
michael@0:     if (state->mode == GZ_READ) {
michael@0:         n = GT_OFF(state->x.have) || (z_off64_t)state->x.have > offset ?
michael@0:             (unsigned)offset : state->x.have;
michael@0:         state->x.have -= n;
michael@0:         state->x.next += n;
michael@0:         state->x.pos += n;
michael@0:         offset -= n;
michael@0:     }
michael@0: 
michael@0:     /* request skip (if not zero) */
michael@0:     if (offset) {
michael@0:         state->seek = 1;
michael@0:         state->skip = offset;
michael@0:     }
michael@0:     return state->x.pos + offset;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off_t ZEXPORT gzseek(file, offset, whence)
michael@0:     gzFile file;
michael@0:     z_off_t offset;
michael@0:     int whence;
michael@0: {
michael@0:     z_off64_t ret;
michael@0: 
michael@0:     ret = gzseek64(file, (z_off64_t)offset, whence);
michael@0:     return ret == (z_off_t)ret ? (z_off_t)ret : -1;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off64_t ZEXPORT gztell64(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return -1;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return -1;
michael@0: 
michael@0:     /* return position */
michael@0:     return state->x.pos + (state->seek ? state->skip : 0);
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off_t ZEXPORT gztell(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     z_off64_t ret;
michael@0: 
michael@0:     ret = gztell64(file);
michael@0:     return ret == (z_off_t)ret ? (z_off_t)ret : -1;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off64_t ZEXPORT gzoffset64(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     z_off64_t offset;
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return -1;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return -1;
michael@0: 
michael@0:     /* compute and return effective offset in file */
michael@0:     offset = LSEEK(state->fd, 0, SEEK_CUR);
michael@0:     if (offset == -1)
michael@0:         return -1;
michael@0:     if (state->mode == GZ_READ)             /* reading */
michael@0:         offset -= state->strm.avail_in;     /* don't count buffered input */
michael@0:     return offset;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: z_off_t ZEXPORT gzoffset(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     z_off64_t ret;
michael@0: 
michael@0:     ret = gzoffset64(file);
michael@0:     return ret == (z_off_t)ret ? (z_off_t)ret : -1;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: int ZEXPORT gzeof(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return 0;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return 0;
michael@0: 
michael@0:     /* return end-of-file state */
michael@0:     return state->mode == GZ_READ ? state->past : 0;
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: const char * ZEXPORT gzerror(file, errnum)
michael@0:     gzFile file;
michael@0:     int *errnum;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return NULL;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return NULL;
michael@0: 
michael@0:     /* return error information */
michael@0:     if (errnum != NULL)
michael@0:         *errnum = state->err;
michael@0:     return state->err == Z_MEM_ERROR ? "out of memory" :
michael@0:                                        (state->msg == NULL ? "" : state->msg);
michael@0: }
michael@0: 
michael@0: /* -- see zlib.h -- */
michael@0: void ZEXPORT gzclearerr(file)
michael@0:     gzFile file;
michael@0: {
michael@0:     gz_statep state;
michael@0: 
michael@0:     /* get internal structure and check integrity */
michael@0:     if (file == NULL)
michael@0:         return;
michael@0:     state = (gz_statep)file;
michael@0:     if (state->mode != GZ_READ && state->mode != GZ_WRITE)
michael@0:         return;
michael@0: 
michael@0:     /* clear error and end-of-file */
michael@0:     if (state->mode == GZ_READ) {
michael@0:         state->eof = 0;
michael@0:         state->past = 0;
michael@0:     }
michael@0:     gz_error(state, Z_OK, NULL);
michael@0: }
michael@0: 
michael@0: /* Create an error message in allocated memory and set state->err and
michael@0:    state->msg accordingly.  Free any previous error message already there.  Do
michael@0:    not try to free or allocate space if the error is Z_MEM_ERROR (out of
michael@0:    memory).  Simply save the error message as a static string.  If there is an
michael@0:    allocation failure constructing the error message, then convert the error to
michael@0:    out of memory. */
michael@0: void ZLIB_INTERNAL gz_error(state, err, msg)
michael@0:     gz_statep state;
michael@0:     int err;
michael@0:     const char *msg;
michael@0: {
michael@0:     /* free previously allocated message and clear */
michael@0:     if (state->msg != NULL) {
michael@0:         if (state->err != Z_MEM_ERROR)
michael@0:             free(state->msg);
michael@0:         state->msg = NULL;
michael@0:     }
michael@0: 
michael@0:     /* if fatal, set state->x.have to 0 so that the gzgetc() macro fails */
michael@0:     if (err != Z_OK && err != Z_BUF_ERROR)
michael@0:         state->x.have = 0;
michael@0: 
michael@0:     /* set error code, and if no message, then done */
michael@0:     state->err = err;
michael@0:     if (msg == NULL)
michael@0:         return;
michael@0: 
michael@0:     /* for an out of memory error, return literal string when requested */
michael@0:     if (err == Z_MEM_ERROR)
michael@0:         return;
michael@0: 
michael@0:     /* construct error message with path */
michael@0:     if ((state->msg = (char *)malloc(strlen(state->path) + strlen(msg) + 3)) ==
michael@0:             NULL) {
michael@0:         state->err = Z_MEM_ERROR;
michael@0:         return;
michael@0:     }
michael@0: #if !defined(NO_snprintf) && !defined(NO_vsnprintf)
michael@0:     snprintf(state->msg, strlen(state->path) + strlen(msg) + 3,
michael@0:              "%s%s%s", state->path, ": ", msg);
michael@0: #else
michael@0:     strcpy(state->msg, state->path);
michael@0:     strcat(state->msg, ": ");
michael@0:     strcat(state->msg, msg);
michael@0: #endif
michael@0:     return;
michael@0: }
michael@0: 
michael@0: #ifndef INT_MAX
michael@0: /* portably return maximum value for an int (when limits.h presumed not
michael@0:    available) -- we need to do this to cover cases where 2's complement not
michael@0:    used, since C standard permits 1's complement and sign-bit representations,
michael@0:    otherwise we could just use ((unsigned)-1) >> 1 */
michael@0: unsigned ZLIB_INTERNAL gz_intmax()
michael@0: {
michael@0:     unsigned p, q;
michael@0: 
michael@0:     p = 1;
michael@0:     do {
michael@0:         q = p;
michael@0:         p <<= 1;
michael@0:         p++;
michael@0:     } while (p > q);
michael@0:     return q >> 1;
michael@0: }
michael@0: #endif