feat(rle-pack): add support for custom input word sizes

thi-ng · Aug 9, 2018 · fd8e761 · fd8e761
1 parent 4fdd3c9
commit fd8e761
Showing 1 changed file with 35 additions and 21 deletions.
diff --git a/packages/rle-pack/src/index.ts b/packages/rle-pack/src/index.ts
@@ -2,53 +2,67 @@ import { BitInputStream, BitOutputStream } from "@thi.ng/bitstream";
 
 const RLE_SIZES = [3, 4, 8, 16];
 
-export function encodeBytes(src: Uint8Array) {
-    const stream = new BitOutputStream().write(src.length, 32);
-    let num = src.length - 1;
-    let val = src[0];
+/**
+ * Compresses input using dynamically sized RLE compression and returns
+ * result as `Uint8Array`.
+ *
+ * @param src
+ * @param num number of input words
+ * @param wordSize in bits, MUST be <= 8
+ */
+export function encodeBytes(src: Iterable<number>, num: number, wordSize = 8) {
+    const stream = new BitOutputStream(num * wordSize / 8).write(num, 32);
+    const n1 = num - 1;
+    let val;
     let tail = true;
     let n = -1;
-    let x, i, t;
+    let i = 0, t;
     const write = () => {
         stream.write(n > 0 ? 1 : 0, 1);
-        stream.write(val, 8);
+        stream.write(val, wordSize);
         if (n > 0) {
             t = (n < 0x8) ? 0 : (n < 0x10) ? 1 : (n < 0x100) ? 2 : 3;
             stream.write(t, 2);
             stream.write(n, RLE_SIZES[t]);
         }
         n = 0;
     };
-    for (i = 0; i <= num; i++) {
-        x = src[i];
-        if (x !== val) {
+    for (let x of src) {
+        if (val === undefined) {
+            val = x;
+        } else if (x !== val) {
             write();
             val = x;
         } else {
             if (++n === 0x10000) {
                 write();
-                tail = (i < num);
+                tail = (i < n1);
             }
         }
+        i++;
+    }
+    if (tail) {
+        write();
     }
-    if (tail) { write(); }
     return stream.bytes();
 }
 
-export function decodeBytes(src: Uint8Array) {
-    let num = (src[0] << 24 | src[1] << 16 | src[2] << 8 | src[3]);
-    let input = new BitInputStream(src, 32);
-    let out = new Uint8Array(num);
-    let i = 0;
+export function decodeBytes(src: Uint8Array, wordSize = 8) {
+    const input = new BitInputStream(src);
+    const ws1 = wordSize + 1;
+    const num = input.read(32);
+    const out = new Uint8Array(num);
+    const flag = 1 << wordSize;
+    const mask = flag - 1;
     let x, j;
-    while (i < num) {
-        x = input.read(9);
-        if (x & 0x100) {
+    for (let i = 0; i < num;) {
+        x = input.read(ws1);
+        if (x & flag) {
             j = i + 1 + input.read(RLE_SIZES[input.read(2)]);
-            out.fill(x & 0xff, i, j);
+            out.fill(x & mask, i, j);
             i = j;
         } else {
-            out[i++] = x & 0xff;
+            out[i++] = x & mask;
         }
     }
     return out;