Hi Gerd
If starting with unsigned deltas in polyline encoding, and attempting
to reduce the length by testing reduced x/yBase values, there isn't any
point in testing Base-1, as the normal number of bits will be the same
(added sign bit) and there will be some overflows.
Patch attached to change this - it gives me a very slight reduction in
RGN size and might give a performance improvement (I didn't detect
any).
I've also fixed a couple of log. logic errors and changed minDx/y
initial to 0, which is much less confusing because they are symmetric
with maxDx/y which do use 0.
Ticker
Index: src/uk/me/parabola/imgfmt/app/trergn/LinePreparer.java
===================================================================
--- src/uk/me/parabola/imgfmt/app/trergn/LinePreparer.java (revision 4644)
+++ src/uk/me/parabola/imgfmt/app/trergn/LinePreparer.java (working copy)
@@ -75,16 +75,20 @@
BitWriter bsBest = bsSimple;
int xBestBase = xBase;
int yBestBase = yBase;
- if (xBase > 0 || yBase > 0 && log.isDebugEnabled()) {
+ if ((xBase > 0 || yBase > 0) && log.isDebugEnabled()) {
log.debug("start opt:", xBase, yBase, xSameSign, xSignNegative, ySameSign, ySignNegative);
}
if (xBase > 0){
int notBetter = 0;
+ int xTestBase = xBase-1;
boolean xSameSignBak = xSameSign;
- xSameSign = false;
- for (int xTestBase = xBase-1; xTestBase >= 0; xTestBase--){
+ if (xSameSign) {
+ xSameSign = false;
+ --xTestBase; // changing to signed will add a bit to each node so xBase-1 can't give saving
+ }
+ for ( ; xTestBase >= 0; xTestBase--){
BitWriter bstest = makeBitStream(minPointsRequired, xTestBase, yBase);
- if (bstest.getBitPosition() >= bsBest.getBitPosition() ){
+ if (bstest.getBitPosition() >= bsBest.getBitPosition()){
if (++notBetter >= 2)
break; // give up
} else {
@@ -97,9 +101,13 @@
}
if (yBase > 0){
int notBetter = 0;
+ int yTestBase = yBase-1;
boolean ySameSignBak = ySameSign;
- ySameSign = false;
- for (int yTestBase = yBase-1; yTestBase >= 0; yTestBase--){
+ if (ySameSign) {
+ ySameSign = false;
+ --yTestBase; // changing to signed will add a bit to each node so yBase-1 can't give saving
+ }
+ for ( ; yTestBase >= 0; yTestBase--){
BitWriter bstest = makeBitStream(minPointsRequired, xBestBase, yTestBase);
if (bstest.getBitPosition() >= bsBest.getBitPosition()){
if (++notBetter >= 2)
@@ -112,7 +120,7 @@
}
ySameSign = ySameSignBak;
}
- if (xBase != xBestBase || yBestBase != yBase && log.isInfoEnabled()) {
+ if ((xBase != xBestBase || yBestBase != yBase) && log.isInfoEnabled()) {
if (bsSimple.getLength() > bsBest.getLength())
log.info("optimizer reduced bit stream byte length from",bsSimple.getLength(),"->",bsBest.getLength(),"(" + (bsSimple.getLength()-bsBest.getLength()), "byte(s)) for",polyline.getClass().getSimpleName(),"with",polyline.getPoints().size(),"points");
else
@@ -252,8 +260,8 @@
// OK go through the points
int lastLat = 0;
int lastLong = 0;
- int minDx = Integer.MAX_VALUE, maxDx = 0;
- int minDy = Integer.MAX_VALUE, maxDy = 0;
+ int minDx = 0, maxDx = 0;
+ int minDy = 0, maxDy = 0;
// index of first point in a series of identical coords (after shift)
int firstsame = 0;
for (int i = 0; i < numPointsToUse; i++) {
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