Have gz_skip() update how far it got for later continuation.

This also simplifies seek processing in general.

4 files changed, 46 insertions, 76 deletions

diff --git a/gzguts.h b/gzguts.h
index 71dea74..69c77eb 100644
--- a/gzguts.h
+++ b/gzguts.h
@@ -193,7 +193,6 @@ typedef struct {
     int reset;              /* true if a reset is pending after a Z_FINISH */
         /* seek request */
     z_off64_t skip;         /* amount to skip (already rewound if backwards) */
-    int seek;               /* true if seek request pending */
         /* error information */
     int err;                /* error code */
     char *msg;              /* error message */
diff --git a/gzlib.c b/gzlib.c
index baa3e79..2f9cdd4 100644
--- a/gzlib.c
+++ b/gzlib.c
@@ -75,7 +75,7 @@ local void gz_reset(gz_statep state) {
     }
     else                            /* for writing ... */
         state->reset = 0;           /* no deflateReset pending */
-    state->seek = 0;                /* no seek request pending */
+    state->skip = 0;                /* no seek request pending */
     gz_error(state, Z_OK, NULL);    /* clear error */
     state->x.pos = 0;               /* no uncompressed data yet */
     state->strm.avail_in = 0;       /* no input data yet */
@@ -362,9 +362,10 @@ z_off64_t ZEXPORT gzseek64(gzFile file, z_off64_t offset, int whence) {
     /* normalize offset to a SEEK_CUR specification */
     if (whence == SEEK_SET)
         offset -= state->x.pos;
-    else if (state->seek)
-        offset += state->skip;
-    state->seek = 0;
+    else {
+        offset += state->past ? 0 : state->skip;
+        state->skip = 0;
+    }
 
     /* if within raw area while reading, just go there */
     if (state->mode == GZ_READ && state->how == COPY &&
@@ -375,7 +376,7 @@ z_off64_t ZEXPORT gzseek64(gzFile file, z_off64_t offset, int whence) {
         state->x.have = 0;
         state->eof = 0;
         state->past = 0;
-        state->seek = 0;
+        state->skip = 0;
         gz_error(state, Z_OK, NULL);
         state->strm.avail_in = 0;
         state->x.pos += offset;
@@ -404,10 +405,7 @@ z_off64_t ZEXPORT gzseek64(gzFile file, z_off64_t offset, int whence) {
     }
 
     /* request skip (if not zero) */
-    if (offset) {
-        state->seek = 1;
-        state->skip = offset;
-    }
+    state->skip = offset;
     return state->x.pos + offset;
 }
 
@@ -431,7 +429,7 @@ z_off64_t ZEXPORT gztell64(gzFile file) {
         return -1;
 
     /* return position */
-    return state->x.pos + (state->seek ? state->skip : 0);
+    return state->x.pos + (state->past ? 0 : state->skip);
 }
 
 /* -- see zlib.h -- */
diff --git a/gzread.c b/gzread.c
index d2ab6b1..5edecbf 100644
--- a/gzread.c
+++ b/gzread.c
@@ -234,20 +234,22 @@ local int gz_fetch(gz_statep state) {
     return 0;
 }
 
-/* Skip len uncompressed bytes of output.  Return -1 on error, 0 on success. */
-local int gz_skip(gz_statep state, z_off64_t len) {
+/* Skip state->skip (> 0) uncompressed bytes of output.  Return -1 on error, 0
+  on success. */
+local int gz_skip(gz_statep state) {
     unsigned n;
 
     /* skip over len bytes or reach end-of-file, whichever comes first */
-    while (len)
+    do {
         /* skip over whatever is in output buffer */
         if (state->x.have) {
-            n = GT_OFF(state->x.have) || (z_off64_t)state->x.have > len ?
-                (unsigned)len : state->x.have;
+            n = GT_OFF(state->x.have) ||
+            (z_off64_t)state->x.have > state->skip ?
+            (unsigned)state->skip : state->x.have;
             state->x.have -= n;
             state->x.next += n;
             state->x.pos += n;
-            len -= n;
+            state->skip -= n;
         }
 
         /* output buffer empty -- return if we're at the end of the input */
@@ -260,6 +262,7 @@ local int gz_skip(gz_statep state, z_off64_t len) {
             if (gz_fetch(state) == -1)
                 return -1;
         }
+    } while (state->skip);
     return 0;
 }
 
@@ -276,11 +279,8 @@ local z_size_t gz_read(gz_statep state, voidp buf, z_size_t len) {
         return 0;
 
     /* process a skip request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_skip(state, state->skip) == -1)
-            return 0;
-    }
+    if (state->skip && gz_skip(state) == -1)
+        return 0;
 
     /* get len bytes to buf, or less than len if at the end */
     got = 0;
@@ -456,11 +456,8 @@ int ZEXPORT gzungetc(int c, gzFile file) {
         return -1;
 
     /* process a skip request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_skip(state, state->skip) == -1)
-            return -1;
-    }
+    if (state->skip && gz_skip(state) == -1)
+        return -1;
 
     /* can't push EOF */
     if (c < 0)
@@ -516,11 +513,8 @@ char * ZEXPORT gzgets(gzFile file, char *buf, int len) {
         return NULL;
 
     /* process a skip request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_skip(state, state->skip) == -1)
-            return NULL;
-    }
+    if (state->skip && gz_skip(state) == -1)
+        return NULL;
 
     /* copy output bytes up to new line or len - 1, whichever comes first --
        append a terminating zero to the string (we don't check for a zero in
diff --git a/gzwrite.c b/gzwrite.c
index 435b462..ef9ffee 100644
--- a/gzwrite.c
+++ b/gzwrite.c
@@ -138,9 +138,9 @@ local int gz_comp(gz_statep state, int flush) {
     return 0;
 }
 
-/* Compress len zeros to output.  Return -1 on a write error or memory
-   allocation failure by gz_comp(), or 0 on success. */
-local int gz_zero(gz_statep state, z_off64_t len) {
+/* Compress state->skip (> 0) zeros to output.  Return -1 on a write error or
+   memory allocation failure by gz_comp(), or 0 on success. */
+local int gz_zero(gz_statep state) {
     int first;
     unsigned n;
     z_streamp strm = &(state->strm);
@@ -149,11 +149,11 @@ local int gz_zero(gz_statep state, z_off64_t len) {
     if (strm->avail_in && gz_comp(state, Z_NO_FLUSH) == -1)
         return -1;
 
-    /* compress len zeros (len guaranteed > 0) */
+    /* compress state->skip zeros */
     first = 1;
-    while (len) {
-        n = GT_OFF(state->size) || (z_off64_t)state->size > len ?
-            (unsigned)len : state->size;
+    do {
+        n = GT_OFF(state->size) || (z_off64_t)state->size > state->skip ?
+            (unsigned)state->skip : state->size;
         if (first) {
             memset(state->in, 0, n);
             first = 0;
@@ -163,8 +163,8 @@ local int gz_zero(gz_statep state, z_off64_t len) {
         state->x.pos += n;
         if (gz_comp(state, Z_NO_FLUSH) == -1)
             return -1;
-        len -= n;
-    }
+        state->skip -= n;
+    } while (state->skip);
     return 0;
 }
 
@@ -182,11 +182,8 @@ local z_size_t gz_write(gz_statep state, voidpc buf, z_size_t len) {
         return 0;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return 0;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return 0;
 
     /* for small len, copy to input buffer, otherwise compress directly */
     if (len < state->size) {
@@ -301,11 +298,8 @@ int ZEXPORT gzputc(gzFile file, int c) {
         return -1;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return -1;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return -1;
 
     /* try writing to input buffer for speed (state->size == 0 if buffer not
        initialized) */
@@ -378,11 +372,8 @@ int ZEXPORTVA gzvprintf(gzFile file, const char *format, va_list va) {
         return state->err;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return state->err;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return state->err;
 
     /* do the printf() into the input buffer, put length in len -- the input
        buffer is double-sized just for this function, so there is guaranteed to
@@ -468,11 +459,8 @@ int ZEXPORTVA gzprintf(gzFile file, const char *format, int a1, int a2, int a3,
         return state->error;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return state->error;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return state->error;
 
     /* do the printf() into the input buffer, put length in len -- the input
        buffer is double-sized just for this function, so there is guaranteed to
@@ -542,11 +530,8 @@ int ZEXPORT gzflush(gzFile file, int flush) {
         return Z_STREAM_ERROR;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return state->err;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return state->err;
 
     /* compress remaining data with requested flush */
     (void)gz_comp(state, flush);
@@ -573,11 +558,8 @@ int ZEXPORT gzsetparams(gzFile file, int level, int strategy) {
         return Z_OK;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            return state->err;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        return state->err;
 
     /* change compression parameters for subsequent input */
     if (state->size) {
@@ -606,11 +588,8 @@ int ZEXPORT gzclose_w(gzFile file) {
         return Z_STREAM_ERROR;
 
     /* check for seek request */
-    if (state->seek) {
-        state->seek = 0;
-        if (gz_zero(state, state->skip) == -1)
-            ret = state->err;
-    }
+    if (state->skip && gz_zero(state) == -1)
+        ret = state->err;
 
     /* flush, free memory, and close file */
     if (gz_comp(state, Z_FINISH) == -1)