From a6c49a2ef920a7fb4cee7181d3bad6206851944d Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sat, 7 Jan 2023 17:52:14 -0800
Subject: [PATCH] oh ho

---
 silly.js | 58 ++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 37 insertions(+), 21 deletions(-)

diff --git a/silly.js b/silly.js
index 9d80ee8..6b4563a 100644
--- a/silly.js
+++ b/silly.js
@@ -4,19 +4,22 @@
 let logBits = 8;
 let logEntries = 2 ** logBits;
 
-let powBits = 16;
-let powEntries = (2 ** powBits);
+let powBits = 19;
+let powEntries = 2 ** powBits;
 
 // Room to hold powers up to 4
-let shift = 4;
+let shift = 3;
 let base = 2 ** (powBits - shift);
 
 // 16-bit lookup table
-let reduction = 0;
+let reduction = 7;
 
 // 12-bit lookup table
 //let reduction = 4;
 
+let powCount = powEntries >> reduction;
+
+
 function toFixed(float) {
     return Math.round(float * base);
 }
@@ -26,7 +29,7 @@ function toFloat(fixed) {
 }
 
 // 256x2 = 512 bytes
-let enloggen = new Uint16Array(logEntries);
+let enloggen = new Uint32Array(logEntries);
 for (let i = 0; i < logEntries; i++) {
     enloggen[i] = toFixed(Math.log2(i));
 }
@@ -35,7 +38,6 @@ for (let i = 0; i < logEntries; i++) {
 // 64kx2 = 128 KiB
 // can reduce number by reducing precision
 // or splitting into high & low vals
-let powCount = powEntries >> reduction;
 let empower = new Uint16Array(powCount);
 for (let i = 0; i < powCount; i++) {
     let fixed = i << reduction;
@@ -43,12 +45,12 @@ for (let i = 0; i < powCount; i++) {
 }
 
 
-// returns fixed
-function log2(byte) {
-    return enloggen[byte];
+// returns fixed point
+function log2(val) {
+    return enloggen[val];
 }
 
-// returns 16-bit number
+// returns rounded integer
 function pow2(fixed) {
     n = (fixed >> reduction);
     return empower[n];
@@ -62,17 +64,16 @@ function mul(a, b) {
     return pow2(la + lb);
 }
 
-/*
 for (let i = 0; i < logEntries; i++) {
     let l = log2(i);
     let p = pow2(l);
-    console.log(`${i} ${l} ${p}`)
+    //console.log(`${i} ${l} ${p}`)
     if (i !== p) {
         //console.log(`mismatch ${i} expected, got ${p} via log value ${l} (${toFloat(l)})`);
     }
 }
-process.exit(1);
-*/
+//process.exit(1);
+
 
 // now just try multipling numbers
 let deltas = 0;
@@ -84,9 +85,15 @@ function round(n, x) {
     return Math.round(x * n) / n;
 }
 
+/*
 while (true) {
     let a = Math.trunc(Math.random() * logEntries);
     let b = Math.trunc(Math.random() * logEntries);
+*/
+
+for (let i = 0; i < 65536; i++) {
+    let a = i & 0xff;
+    let b = (i >> 8) & 0xff;
     let expected = a * b;
     let result = mul(a, b);
 
@@ -102,13 +109,22 @@ while (true) {
         //console.log(`${a} * ${b} = ${result}`);
     }
     count++;
-    if (count == 100) {
-        deltaAvg = deltas / deltaCount;
-        console.log(`${count - deltaCount} of ${count} ok -- ${deltaCount} off by avg ${round(10,deltaAvg)})`);
-        count = 0;
-        deltas = 0;
-        deltaCount = 0;
-    }
 }
 
+deltaAvg = deltas / deltaCount;
+console.log(`${count - deltaCount} of ${count} ok -- ${deltaCount} off by avg ${round(10,deltaAvg)})`);
+count = 0;
+deltas = 0;
+deltaCount = 0;
+
 console.log('done');
+
+
+console.log(`size of enloggen table: ${enloggen.length} entries, ${enloggen.length * 3} bytes`);
+console.log(`size of empower table: ${empower.length} entries, ${empower.length * 2} bytes`);
+
+let m = 0;
+for (let i = 0; i < enloggen.length; i++) {
+    m = Math.max(m, enloggen[i]);
+}
+console.log(`max enloggen entry is ${m}`);