guest271314 · August 17, 2025 18:45 · Aug 17, 2025 · Aug 15, 2025
diff --git a/hex-from-array.md b/hex-from-array.md
@@ -1,3 +1,5 @@
+From discord, AssemblyScript channel
+
 > guest271314 Let's say you have a `TypedArray` such as `var u = Uint8Array.of(49, 48, 48, 48)` 
 and you know those values in hexidecimal will produce an integer 
 `parseInt(new TextDecoder().decode(u), 16) // 4096`. How can that `4096` 

diff --git a/hex-from-array.md b/hex-from-array.md
@@ -0,0 +1,40 @@
+> guest271314 Let's say you have a `TypedArray` such as `var u = Uint8Array.of(49, 48, 48, 48)` 
+and you know those values in hexidecimal will produce an integer 
+`parseInt(new TextDecoder().decode(u), 16) // 4096`. How can that `4096` 
+be derived without converting to a string, using `DataView` or other methods to get the integer?
+
+> PhoenixIllusion case insensitive ascii-to-hex could be brute forced via:
+```js
+function hexFromArray(a) {
+  let total = 0;
+  for(let i=0;i<a.length;i++) {
+    hex = a[i];
+    const intVal = hex > 96 ? hex - 87 : hex > 64 ? hex - 55 : hex - 48;
+    total = intVal + (total << 4);
+  }
+  return total;
+}
+```
+> or taking advantage of the fact the lower 4 bits of both '0', 'a', and 'A' are fairly clean,
+for `0-9` = ascii & 0xF
+for `a-f` or `A-F` = (ascii & 0xF) + 9
+```js
+function hexFromArray(a) {
+  let total = 0;
+  for(let i=0;i<a.length;i++) {
+    let hex = a[i];
+    let intVal = hex & 0xF;
+    if (hex > 64) intVal += 9;
+    total = intVal + (total << 4);
+  }
+  return total;
+}
+```
+> pretty sure this isn't more efficient since trading a conditional jump for a 100% always triggering 
+shift+multiply+add, but branchless
+```
+const hex = a[i];
+const intVal = hex & 0xF;
+const a_f = (hex >> 6) * 9;
+total = (intVal + a_f) + (total << 4);
+```