Improve speed of gzprintf() in transparent mode.

gzguts.h

@@ -170,7 +170,7 @@ typedef struct {
     char *path;             /* path or fd for error messages */
     unsigned size;          /* buffer size, zero if not allocated yet */
     unsigned want;          /* requested buffer size, default is GZBUFSIZE */
-    unsigned char *in;      /* input buffer */
+    unsigned char *in;      /* input buffer (double-sized when writing) */
     unsigned char *out;     /* output buffer (double-sized when reading) */
     int direct;             /* 0 if processing gzip, 1 if transparent */
         /* just for reading */

gzlib.c

@@ -331,6 +331,8 @@ int ZEXPORT gzbuffer(file, size)
         return -1;
 
     /* check and set requested size */
+    if ((size << 1) < size)
+        return -1;              /* need to be able to double it */
     if (size < 2)
         size = 2;               /* need two bytes to check magic header */
     state->want = size;

gzwrite.c

@@ -18,8 +18,8 @@ local int gz_init(state)
     int ret;
     z_streamp strm = &(state->strm);
 
-    /* allocate input buffer */
-    state->in = (unsigned char *)malloc(state->want);
+    /* allocate input buffer (double size for gzprintf) */
+    state->in = (unsigned char *)malloc(state->want << 1);
     if (state->in == NULL) {
         gz_error(state, Z_MEM_ERROR, "out of memory");
         return -1;
@@ -309,7 +309,8 @@ int ZEXPORT gzputs(file, str)
 /* -- see zlib.h -- */
 int ZEXPORTVA gzvprintf(gzFile file, const char *format, va_list va)
 {
-    int size, len;
+    unsigned len, left;
+    char *next;
     gz_statep state;
     z_streamp strm;
 
@@ -334,39 +335,47 @@ int ZEXPORTVA gzvprintf(gzFile file, const char *format, va_list va)
             return 0;
     }
 
-    /* consume whatever's left in the input buffer */
-    if (strm->avail_in && gz_comp(state, Z_NO_FLUSH) == -1)
-        return 0;
-
-    /* do the printf() into the input buffer, put length in len */
-    size = (int)(state->size);
-    state->in[size - 1] = 0;
+    /* 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
+       be state->size bytes available after the current contents */
+    if (strm->avail_in == 0)
+        strm->next_in = state->in;
+    next = (char *)(strm->next_in + strm->avail_in);
+    next[state->size - 1] = 0;
 #ifdef NO_vsnprintf
 #  ifdef HAS_vsprintf_void
-    (void)vsprintf((char *)(state->in), format, va);
-    for (len = 0; len < size; len++)
-        if (state->in[len] == 0) break;
+    (void)vsprintf(next, format, va);
+    for (len = 0; len < state->size; len++)
+        if (next[len] == 0) break;
 #  else
-    len = vsprintf((char *)(state->in), format, va);
+    len = vsprintf(next, format, va);
 #  endif
 #else
 #  ifdef HAS_vsnprintf_void
-    (void)vsnprintf((char *)(state->in), size, format, va);
-    len = strlen((char *)(state->in));
+    (void)vsnprintf(next, state->size, format, va);
+    len = strlen(next);
 #  else
-    len = vsnprintf((char *)(state->in), size, format, va);
+    len = vsnprintf(next, state->size, format, va);
 #  endif
 #endif
 
     /* check that printf() results fit in buffer */
-    if (len <= 0 || len >= (int)size || state->in[size - 1] != 0)
+    if (len == 0 || len >= state->size || next[state->size - 1] != 0)
         return 0;
 
-    /* update buffer and position, defer compression until needed */
-    strm->avail_in = (unsigned)len;
-    strm->next_in = state->in;
+    /* update buffer and position, compress first half if past that */
+    strm->avail_in += len;
     state->x.pos += len;
-    return len;
+    if (strm->avail_in >= state->size) {
+        left = strm->avail_in - state->size;
+        strm->avail_in = state->size;
+        if (gz_comp(state, Z_NO_FLUSH) == -1)
+            return 0;
+        memcpy(state->in, state->in + state->size, left);
+        strm->next_in = state->in;
+        strm->avail_in = left;
+    }
+    return (int)len;
 }
 
 int ZEXPORTVA gzprintf(gzFile file, const char *format, ...)
@@ -390,7 +399,8 @@ int ZEXPORTVA gzprintf (file, format, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10,
     int a1, a2, a3, a4, a5, a6, a7, a8, a9, a10,
         a11, a12, a13, a14, a15, a16, a17, a18, a19, a20;
 {
-    int size, len;
+    unsigned len, left;
+    char *next;
     gz_statep state;
     z_streamp strm;
 
@@ -419,44 +429,52 @@ int ZEXPORTVA gzprintf (file, format, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10,
             return 0;
     }
 
-    /* consume whatever's left in the input buffer */
-    if (strm->avail_in && gz_comp(state, Z_NO_FLUSH) == -1)
-        return 0;
-
-    /* do the printf() into the input buffer, put length in len */
-    size = (int)(state->size);
-    state->in[size - 1] = 0;
+    /* 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
+       be state->size bytes available after the current contents */
+    if (strm->avail_in == 0)
+        strm->next_in = state->in;
+    next = (char *)(strm->next_in + strm->avail_in);
+    next[state->size - 1] = 0;
 #ifdef NO_snprintf
 #  ifdef HAS_sprintf_void
-    sprintf((char *)(state->in), format, a1, a2, a3, a4, a5, a6, a7, a8,
-            a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20);
+    sprintf(next, format, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12,
+            a13, a14, a15, a16, a17, a18, a19, a20);
     for (len = 0; len < size; len++)
-        if (state->in[len] == 0) break;
+        if (next[len] == 0)
+            break;
 #  else
-    len = sprintf((char *)(state->in), format, a1, a2, a3, a4, a5, a6, a7, a8,
-                  a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20);
+    len = sprintf(next, format, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11,
+                  a12, a13, a14, a15, a16, a17, a18, a19, a20);
 #  endif
 #else
 #  ifdef HAS_snprintf_void
-    snprintf((char *)(state->in), size, format, a1, a2, a3, a4, a5, a6, a7, a8,
-             a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20);
-    len = strlen((char *)(state->in));
+    snprintf(next, state->size, format, a1, a2, a3, a4, a5, a6, a7, a8, a9,
+             a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20);
+    len = strlen(next);
 #  else
-    len = snprintf((char *)(state->in), size, format, a1, a2, a3, a4, a5, a6,
-                   a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18,
-                   a19, a20);
+    len = snprintf(next, state->size, format, a1, a2, a3, a4, a5, a6, a7, a8,
+                   a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20);
 #  endif
 #endif
 
     /* check that printf() results fit in buffer */
-    if (len <= 0 || len >= (int)size || state->in[size - 1] != 0)
+    if (len == 0 || len >= state->size || next[state->size - 1] != 0)
         return 0;
 
-    /* update buffer and position, defer compression until needed */
-    strm->avail_in = (unsigned)len;
-    strm->next_in = state->in;
+    /* update buffer and position, compress first half if past that */
+    strm->avail_in += len;
     state->x.pos += len;
-    return len;
+    if (strm->avail_in >= state->size) {
+        left = strm->avail_in - state->size;
+        strm->avail_in = state->size;
+        if (gz_comp(state, Z_NO_FLUSH) == -1)
+            return 0;
+        memcpy(state->in, state->in + state->size, left);
+        strm->next_in = state->in;
+        strm->avail_in = left;
+    }
+    return (int)len;
 }
 
 #endif

zlib.h

@@ -1291,10 +1291,9 @@ ZEXTERN int ZEXPORT gzbuffer OF((gzFile file, unsigned size));
    default buffer size is 8192 bytes.  This function must be called after
    gzopen() or gzdopen(), and before any other calls that read or write the
    file.  The buffer memory allocation is always deferred to the first read or
-   write.  Two buffers are allocated, either both of the specified size when
-   writing, or one of the specified size and the other twice that size when
-   reading.  A larger buffer size of, for example, 64K or 128K bytes will
-   noticeably increase the speed of decompression (reading).
+   write.  Three times that size in buffer space is allocated.  A larger buffer
+   size of, for example, 64K or 128K bytes will noticeably increase the speed
+   of decompression (reading).
 
      The new buffer size also affects the maximum length for gzprintf().