faster partial reading of file wip

assets/disk0/decodemov.js

@@ -1,54 +1,106 @@
 
 let filename = exec_args[1]
+
 const FBUF_SIZE = 560*448
+const MAGIC = [0x1F, 0x54, 0x53, 0x56, 0x4D, 0x4D, 0x4F, 0x56]
 
 let status = filesystem.open("A", filename, "R")
 if (status) return status
 
 println("Reading...")
 
-let bytes = filesystem.readAllBytes("A")
+//let bytes = filesystem.readAllBytes("A")
 
 con.clear()
 
 let readCount = 0
 
 function readBytes(length) {
-    let ret = new Int8Array(length)
+    /*let ret = new Int8Array(length)
     for (let k = 0; k < length; k++) {
         ret[k] = bytes[readCount]
         readCount += 1
     }
-    return ret
+    return ret*/
+
+    let ptr = sys.malloc(length)
+    let requiredBlocks = (readCount == 0) + Math.floor((readCount + length) / 4096) - Math.floor(readCount / 4096)
+    let port = filesystem._toPorts("A")
+
+    let completedReads = 0
+
+    for (let bc = 0; bc < requiredBlocks; bc++) {
+        if (readCount % 4096 == 0) {
+            com.sendMessage(port[0], "READ")
+            let thisBlockLen = com.fetchResponse(port[0]) // [0, 4095]
+            let remaining = Math.min(4096, length - completedReads)
+
+            // copy from read buffer to designated position
+            sys.memcpy(-4097, ptr + readCount, remaining)
+
+            // increment readCount properly
+            readCount += remaining
+            completedReads += remaining
+        }
+        else {
+            let padding = 4096 - (readCount % 4096)
+            let remaining = Math.min(padding, length - completedReads)
+
+            // copy from read buffer to designated position
+            sys.memcpy(-4097 - padding, ptr + readCount, remaining)
+
+            // increment readCount properly
+            readCount += remaining
+            completedReads += remaining
+        }
+    }
+
+    return ptr
 }
 
 function readInt() {
     let b = readBytes(4)
-    return (b[0] & 255) | ((b[1] & 255) << 8) | ((b[2] & 255) << 16) | ((b[3] & 255) << 24)
+    let i = (sys.peek(b) & 255) | ((sys.peek(b+1) & 255) << 8) | ((sys.peek(b+2) & 255) << 16) | ((sys.peek(b+3) & 255) << 24)
+    sys.free(b)
+    return i
 }
 
 function readShort() {
     let b = readBytes(2)
-    return (b[0] & 255) | ((b[1] & 255) << 8)
+    let i = (sys.peek(b) & 255) | ((sys.peek(b+1) & 255) << 8)
+    sys.free(b)
+    return i
 }
 
 
 let magic = readBytes(8)
 
-if (String.fromCharCode.apply(null, magic) != '\x1fTSVMMOV') return 1
+// check if magic number matches
+MAGIC.forEach((b,i) => {
+    if (sys.peek(magic + i) & 255 != b) return 1
+})
+sys.free(magic)
+
 
 let width = readShort()
 let height = readShort()
 let fps = readShort()
 let frameCount = readInt() % 16777216
 
+serial.println(`Dim: (${width}x${height}), FPS: ${fps}, Frames: ${frameCount}`)
+
 let fbuf = sys.malloc(FBUF_SIZE)
 
 for (let f = 0; f < frameCount; f++) {
+    serial.println(`Frame #${f+1}`)
+
     let payloadLen = readInt()
-    let gzipped = readBytes(payloadLen)
-    gzip.decompTo(gzipped, fbuf)
+    let gzippedPtr = readBytes(payloadLen)
+
+    gzip.decompFromTo(gzippedPtr, payloadLen, fbuf) // should return FBUF_SIZE
+
     dma.ramToFrame(fbuf, 0, FBUF_SIZE)
+    sys.free(gzippedPtr)
 }
 
 sys.free(fbuf)