From: Frédéric Perrin <frederic.perrin@att.com>
Date: Thu, 30 Jan 2020 10:40:32 +0000 (+0000)
Subject: Read ZIP entries in chunks
X-Git-Tag: v19.2.fp6~1^2~3
X-Git-Url: http://gitweb.fperrin.net/?p=GpsPrune.git;a=commitdiff_plain;h=8f45a9f2289e01d4f6eee6036f7fc3c4a92e3024

Read ZIP entries in chunks

Cuts reading a tile from several seconds to pretty much instantaneous.
Particularily noticable with 1-arcsecond datafiles
---

diff --git a/src/tim/prune/function/srtm/SrtmSource.java b/src/tim/prune/function/srtm/SrtmSource.java
index 0791cd8..44ceccf 100644
--- a/src/tim/prune/function/srtm/SrtmSource.java
+++ b/src/tim/prune/function/srtm/SrtmSource.java
@@ -19,11 +19,19 @@ public abstract class SrtmSource {
 		throws IOException
 	{
 		int[] heights = new int[tileSize];
+		int dataSize = 2 * tileSize;
+		byte[] buffer = new byte[dataSize];
 		// Read entire file contents into one byte array
-		for (int i = 0; i < heights.length; i++)
+		int alreadyRead = 0;
+		while (alreadyRead < dataSize)
 		{
-			heights[i] = inStream.read() * 256 + inStream.read();
-			if (heights[i] >= 32768) {heights[i] -= 65536;}
+			alreadyRead += inStream.read(buffer, alreadyRead, dataSize - alreadyRead);
+		}
+		for (int i = 0; i < tileSize; i++)
+		{
+			// Bytes are signed. Cast high-order to int with sign
+			// extension, and clamp low-order to its unsigned range
+			heights[i] = buffer[2 * i] * 256 + (0xff & buffer[2 * i + 1]);
 		}
 		// Close stream
 		inStream.close();