A small opimization to not use temp buffer when size of npoints is not unpredictable

git-svn-id: http://svn.osgeo.org/postgis/trunk@13589 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/liblwgeom/lwout_twkb.c b/liblwgeom/lwout_twkb.c
index c0c6fe13c1664a2d1ba3cbaea4c10a82e884d27e..149b891138346fc770886e3ffb49a44299157772 100644 (file)
--- a/liblwgeom/lwout_twkb.c
+++ b/liblwgeom/lwout_twkb.c
@@ -93,9 +93,10 @@ static int ptarray_to_twkb_buf(const POINTARRAY *pa, TWKB_GLOBALS *globals, TWKB
 {
        int ndims = FLAGS_NDIMS(pa->flags);
        int i, j;
-       bytebuffer_t b;
+       bytebuffer_t b,*b_p;
        int64_t nextdelta[MAX_N_DIMS];
        int npoints = 0;
+       int where2writenpoints=0;
 
        LWDEBUGF(2, "Entered %s", __func__);
 
@@ -106,11 +107,36 @@ static int ptarray_to_twkb_buf(const POINTARRAY *pa, TWKB_GLOBALS *globals, TWKB
                bytebuffer_append_uvarint(ts->geom_buf, pa->npoints);
                return 0;
        }
-               
-       /* Independent buffer to hold the coordinates, so we can put the npoints */
-       /* into the stream once we know how many points we actually have */
-       bytebuffer_init_with_size(&b, 3 * ndims * pa->npoints);
-       
+
+       /*If npoints is more than 127 it is unpredictable how many bytes npoints will need*/
+       /*Then we have to store the deltas in a temp buffer to later add them after npoints*/
+       /*If noints is below 128 we know 1 byte will be needed*/
+       /*Then we can make room for that 1 byte at once and write to*/
+       /*ordinary buffer*/
+       if(pa->npoints>127)
+       {
+               /* Independent buffer to hold the coordinates, so we can put the npoints */
+               /* into the stream once we know how many points we actually have */
+               bytebuffer_init_with_size(&b, 3 * ndims * pa->npoints);
+               b_p=&b;
+       }
+       else
+       {
+               /*We give an alias to our ordinary buffer*/
+               b_p=ts->geom_buf;
+               if ( register_npoints )         
+               {               
+                       /*We do not store a pointer to the place where we want the npoints value*/
+                       /*Instead we store how far from the beginning of the buffer we want the value*/
+                       /*That is because we otherwise will get in trouble if the buffer is reallocated*/                       
+                       where2writenpoints=b_p->writecursor-b_p->buf_start;
+                       
+                       /*We just move the cursor 1 step to make room for npoints byte*/
+                       /*We use the function append_byte even if we have no value yet, */
+                       /*since that gives us the check for big enough buffer and moves the cursor*/
+                       bytebuffer_append_byte(b_p, 0);
+               }
+       }
        for ( i = 0; i < pa->npoints; i++ )
        {
                double *dbl_ptr = (double*)getPoint_internal(pa, i);
@@ -141,7 +167,7 @@ static int ptarray_to_twkb_buf(const POINTARRAY *pa, TWKB_GLOBALS *globals, TWKB
                for ( j = 0; j < ndims; j++ )
                {
                        ts->accum_rels[j] += nextdelta[j];
-                       bytebuffer_append_varint(&b, nextdelta[j]);
+                       bytebuffer_append_varint(b_p, nextdelta[j]);
                }
 
                /* See if this coordinate expands the bounding box */
@@ -159,16 +185,27 @@ static int ptarray_to_twkb_buf(const POINTARRAY *pa, TWKB_GLOBALS *globals, TWKB
 
        }       
 
-       /* Now write the temporary results into the main buffer */
-       /* First the npoints */
-       if ( register_npoints ) 
-               bytebuffer_append_uvarint(ts->geom_buf, npoints);
-       
-       /* Now the coordinates */
-       bytebuffer_append_bytebuffer(ts->geom_buf, &b);
-       
-       /* Clear our temporary buffer */
-       lwfree(b.buf_start);
+
+
+       if(pa->npoints>127)
+       {               
+               /* Now write the temporary results into the main buffer */
+               /* First the npoints */
+               if ( register_npoints ) 
+                       bytebuffer_append_uvarint(ts->geom_buf, npoints);
+               /* Now the coordinates */
+               bytebuffer_append_bytebuffer(ts->geom_buf, b_p);
+               
+               /* Clear our temporary buffer */
+               lwfree(b.buf_start);
+       }
+       else
+       {
+               /*If we didn't use a temp buffer, we just write that npoints value*/
+               /*to where it belongs*/
+               if ( register_npoints ) 
+                       varint_u64_encode_buf(npoints, b_p->buf_start+where2writenpoints);
+       }
        
        return 0;
 }