Floats as written, never fused; fma and muladd; f32/f64 bits, f16 and bf16

- a * b + c is two roundings on every processor and --cpu: the IR has no fast-math flags, and clang
  compiles it with -ffp-contract=on (checked in the assembly: never fused, also with FMA hardware)
- fma(a, b, c) / v.fma(b, c): one rounding, always (llvm.fma)
- muladd(a, b, c) / v.muladd(b, c): the fastest way here (llvm.fmuladd), what v.fma was before
- f32_bits / f32_from_bits / f64_bits / f64_from_bits: bitcasts, also of vectors
- f16_to_f32 / f32_to_f16 (LLVM half), bf16_to_f32 / f32_to_bf16 (integer ops, ties to even, NaN kept)
- docs (en, pl): what is guaranteed about floats, the new built-ins

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Psc42moPLwP43Cmb9oZqSR

docs/en/cheatsheet.md

@@ -259,7 +259,8 @@ Types: `f32x4/8/16`, `f64x2/4/8`, `i8x16/32/64`, `i16x8/16/32`, `i32x4/8/16`, `i
 | `v[i]`, `v[i] = x`, `v.len` | a lane; the number of lanes |
 | `min(v, w)`, `max`, `abs(v)`, `clamp(v, lo, hi)` | lane by lane |
 | `v.sum()`, `v.min()`, `v.max()`, `v.dot(w)` | one number from all the lanes |
-| `v.sqrt()`, `v.floor()`, `v.ceil()`, `v.round()`, `v.fma(b, c)` | every lane (float lanes; `fma` = `v * b + c`) |
+| `v.sqrt()`, `v.floor()`, `v.ceil()`, `v.round()` | every lane (float lanes) |
+| `v.fma(b, c)`, `v.muladd(b, c)` | `v * b + c`: one rounding always / the fastest way here |
 | `v.store(list, i)` | lanes into `list[i]` … |
 
 ---
@@ -324,6 +325,9 @@ Automatic only when nothing is lost: smaller → bigger number, any int → floa
 | `shell(command)` | run a command, its exit code |
 | `exit(code)` | stop the program now (also ends an `or { }` block) |
 | `min(a, b, …)`, `max(a, b, …)`, `abs(x)`, `clamp(x, lo, hi)` | for any numbers (your own function of that name wins) |
+| `fma(a, b, c)`, `muladd(a, b, c)` | `a * b + c` with one rounding / fused where the processor can (`a * b + c` written out is never fused) |
+| `f32_bits(x)`, `f32_from_bits(u)`, `f64_bits`, `f64_from_bits` | a float's bits as `u32`/`u64` and back, unchanged |
+| `f16_to_f32(h)`, `f32_to_f16(x)`, `bf16_to_f32(b)`, `f32_to_bf16(x)` | half and bfloat16 numbers (in a `u16`) ↔ `f32`; also on vectors |
 | `error(message)` | `return error("…")` in a `-> T!` function |
 | `addr(x)` | pointer to x; `addr(fn)` = C callback |
 | `assert(cond)`, `assert(cond, "why")` | stop with a runtime error when cond is false (in a `test` block: that test fails) |