ludic/docs/language/math/math-log.md
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feat(stdlib): Math.exp/log/pow + Ease.elastic transcendentals (issue #25)
Finish the unblocked "Math / Ease" half of #25: the fixed-point
transcendentals deferred from #2. Vec.* stays blocked on the vec2 type
in #1.

- Math.exp, Math.log (natural), Math.pow — deterministic Q16.16 via two
  new prelude fns in emit_math_prelude: @fn_fx_exp2 (range-reduced 5th-order
  Taylor 2^f, then a clamped shift by the integer part) and @fn_fx_log2
  (llvm.ctlz for the exponent + an atanh series on (m-1)/(m+1) for the
  mantissa). exp=2^(x·log2 e), log=log2(x)·ln2, pow=2^(b·log2 a).
- Ease.elastic — ease-out elastic 2^(-10t)·sin((10t-0.75)·2pi/3)+1.
- Pure integer IR, so bit-identical on every platform. Results must fit the
  Q16.16 range (|x| < 32768); larger magnitudes saturate (documented).

Test selfhost/tests/transcend.ludic (registered in the self-host suite) +
docs for all four. Reseeded; the C-free bootstrap fixpoint holds. All suites
green (24 self-host, 45 regression, 29 tool).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-30 01:19:44 +03:00

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---
id: math-log
name: Math.log
category: math
kind: namespace-method
tokens: Math.log
sig: Math.log(x) -> fixed
tip: The natural logarithm of x.
order: 30
ns: Math
member: log
---
Returns the natural logarithm <code>ln(x)</code> for <code>x &gt; 0</code>, computed in Q16.16 from a deterministic integer <code>log₂</code> (bit-scan for the exponent, a short series for the mantissa) scaled by <code>ln 2</code> — bit-identical on every platform. It is the inverse of <code>Math.exp</code>: reach for it to turn multiplicative growth into a straight line — score-to-level curves, logarithmic difficulty, decibel-style volume. Non-positive inputs are out of domain and saturate to a large negative value rather than returning a meaningful number.
```ludic
program Demo {
handler Step phase Update {
let level = Math.floor(Math.log(score)) # diminishing returns on score
}
}
```