hydrogen-web/prototypes/idb-cmp-numbers.html

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<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<style type="text/css">
pre {
font-family: monospace;
display: block;
white-space: pre;
font-size: 2em;
}
</style>
</head>
<body>
<script type="text/javascript">
const MIN = 0;
const MAX = 0xFFFFFFFF;
function zeropad(a, n) {
return "0".repeat(n - a.length) + a;
}
// const encodeNumber = n => zeropad((n >>> 0).toString(16), 8);
function encodeNumber(n) {
const a = (n & 0xFFFF0000) >>> 16;
const b = (n & 0xFFFF) >>> 0;
//return zeropad(a.toString(16), 4) + zeropad(b.toString(16), 4);
return String.fromCharCode(a, b);
}
function decodeNumber(s) {
const a = s.charCodeAt(0);
const b = s.charCodeAt(1);
//return `${a.toString(16)} ${b}`;
return ((a << 16) | b) >>> 0;
}
function formatArg(a) {
if (typeof a === "string") {
return `"${a}"`;
}
if (Array.isArray(a)) {
return `[${a.map(formatArg)}]`;
}
return a+"";
}
function cmp(a, b) {
let value;
try {
const result = indexedDB.cmp(encodeNumber(a), encodeNumber(b));
if (result < 0) {
value = "a < b";
} else if (result === 0) {
value = "a = b";
} else if (result > 0) {
value = "a > b";
}
} catch(err) {
value = err.message;
}
return `cmp(${formatArg(a)} as ${formatArg(encodeNumber(a))},\n ${formatArg(b)} as ${formatArg(encodeNumber(b))}): ${value}`;
}
try {
const tests = [
// see https://stackoverflow.com/questions/28413947/space-efficient-way-to-encode-numbers-as-sortable-strings
// need to encode numbers with base 256 and zero padded at start
// should still fit in 8 bytes then?
(cmp) => cmp(9, 100000),
(cmp) => cmp(1, 2),
(cmp) => cmp(MIN, 1),
(cmp) => cmp(MIN, MIN),
(cmp) => cmp(MIN, MAX),
(cmp) => cmp(MAX >>> 1, MAX),
(cmp) => cmp(0x7fffffff, 0xffff7fff),
(cmp) => cmp(MAX, MAX),
(cmp) => cmp(MAX - 1, MAX),
];
for (const fn of tests) {
const txt = document.createTextNode(fn(cmp));
const p = document.createElement("pre");
p.appendChild(txt);
document.body.appendChild(p);
}
} catch(err) {
alert(err.message);
}
let prev;
for (let i = MIN; i <= MAX; i += 100) {
if (decodeNumber(encodeNumber(i)) !== i) {
document.write(`<p>${i} decodes back to ${decodeNumber(encodeNumber(i))}</p>`);
break;
}
if (typeof prev === "number") {
if (indexedDB.cmp(encodeNumber(prev), encodeNumber(i)) >= 0) {
document.write(`<p>${i} <= ${prev}</p>`);
break;
}
}
prev = i;
}
document.write(`<p>check from ${MIN} to ${prev}</p>`);
</script>
</body>
</html>