implement flashing firmware from new zip format

src/utils/math.ts

@@ -0,0 +1,27 @@
+/**
+ * Compute modulo using floored division
+ * @param a first operand
+ * @param b second operand
+ */
+export function fmod(a: number, b: number): number {
+    let c = a % b;
+    if (c / b < 0) {
+        c += b;
+    }
+    return c;
+}
+
+/**
+ * Calculates the 32-bit "sum complement" checksum
+ * @data an iterable of 32-bit integers
+ * @returns the value that needs to be added to get 0
+ */
+export function sumComplement32(data: Iterable<number>): number {
+    let total = 0;
+    for (const n of data) {
+        total += n;
+        total &= ~0;
+    }
+    // checksum is two's complement of total
+    return ~total + 1;
+}