git:20260821.71d8484 to git:20260918.95c4588

+ Home: `libsrc/math/float/math16/`. Docs of record: `libsrc/math/float/math16/README.md`.

+ Link via **`--math16`** (`-lmath16@{ZCC_LIBCPU}`). Adjunct: no conflict with

+ math32 / math48 / am9511. **No** printf / scanf / dtoa on the math16 product.

+ Classic products match math32’s CPU set: `math16.lib` plus

+ `math16_{ixiy,z80n,z180,ez80_z80,r2ka,r4k,r6k,kc160,8085,8080,gbz80}.lib`.

+ 8080 / 8085 / gbz80 higher via **sccz80 only**.

+

+ ### Layout

+

+ | Tree | Role |

+ |------|------|

+ | `asm/` | 8080-compatible shared files (specials, coeff). Classic: `newlibfiles_common_asm.lst` |

+ | `asm/z80/` | Z80-family cores; z80n/z180/ez80_z80/r2ka/kc160 assemble this list. Unrolled 11×11 / 16×16 is `IF __CPU_Z80__` only; others call `l_mulu_32_16x16`. `asm_f16_f48` is Z80-only |

+ | `asm/8085/`, `asm/8080/`, `asm/gbz80/` | Stack-only CPU cores (same one-op-per-file map) |

+ | `c/z80/`, `c/8085/`, `c/8080/`, `c/gbz80/` | Higher functions. 8080/8085/gbz80 via **sccz80 only**. Binary-op bridges that use EXX live in `c/sccz80` (z80) or `c/<cpu>` (8080/8085/gbz80). No 8085 `fma` |

+ | `newlibfiles_*.lst` | Classic products. All Z80-family CPUs use `@newlibfiles_z80.lst` (no per-CPU mul-helper lists) |

+ | `math16_z80_asm.lst` + `math16_{sccz80,sdcc,c_asm}.lst` | Newlib clib embed only. No 8085/8080/gbz80 newlib math16 list |

+

+ Policy mirrors math32:

+

+ In **C higher functions** (`c/*.c`):

+

+ | Need | Write | Do not write |

+ |------|--------|----------------|

+ | Reciprocal `1/n` | `1.0/x` (restoring `div`) | `invf16(x)` |

+ | Inverse square root | `invsqrtf16(x)` | `1.0/sqrtf16(x)` |

+ | Square `x*x` | `sqrf16(x)` (fastcall, always +) | `mulf16(x,x)` / a `sqrf16` macro |

+ | IEEE bits | `union float16_int` from `c/math16.h` | a local `uint16_t` union |

+

+ `pow(x, -0.5)` keeps `invsqrtf16`. Packed-half hi byte after abs: `|x|>=128` iff `m16_ieee_hi >= 0x58`. Do not fmod for `|x|<128`.

+

+ 5. Suite: `make -C test/suites/math test_math16.bin test_math16_z180.bin test_math16_ez80_z80.bin test_math16_z80n.bin test_math16_r2ka.bin test_math16_r4k.bin test_math16_r6k.bin test_math16_kc160.bin test_math16_8085.bin test_math16_8080.bin test_math16_gbz80.bin`. Newlib: `+rc2014 -clib=new` with `-lmath16 -lmath32` (mirror math32 rc2014 recipe).

+ 6. Higher funcs layout: `c/z80/` (sccz80 +new), `c/8085/`, `c/8080/`, `c/gbz80/`. **`c/Makefile` clean:** only remove C-derived `*.asm` in those dirs (`$(AFILES8085)` / `$(AFILES8080)` / `$(AFILESGBZ80)`); keep hand-written `cm16_sccz80_*.asm`.

+ 7. Cores: `asm/{z80,8085,8080,gbz80}/`. Packed `*` / `sqrf16` = 11×11 (`asm_f16_mul_callee` / `asm_f16_sqr`). Poly, inv, sqrt NR, hypot, fma = f24 16×16 (`asm_f24_mul_f24`).

+ 8. Unrolled 11×11 / 16×16 mulu is **`IF __CPU_Z80__` only**. z80n / z180 / ez80 / kc160 / rabbit call **`l_mulu_32_16x16`** (HW integer). Do not assemble the unrolled body into those products.

+ 9. `--math16` is **adjunct** (no conflict with math32/math48). Classic: `math16.lib` + `math16_{8085,8080,gbz80,…}.lib`. Newlib sccz80 **bakes math16 into `lib/clibs/sccz80/z80.lib`**. After core edits: delete `*math16*` `.o` under `libsrc/newlib/target/{math16,z80}/obj`, then `make -C libsrc/newlib math16 z80`. Prove `cm16_sccz80_mul_callee` is `G =` onto `asm_f16_mul_callee` (stale is `G A` at a later line).

+ 10. Classic 8085/8080/gbz80 Makefile targets have **no OBJECTS deps**. `rm` `obj/<cpu>/…/asm_f16_*.o` and `libsrc/math16*.lib`, then `make -C libsrc math16.lib` and `cp` into `lib/clibs/`. `fromfix16` / `tofix16` are Z80-family only (no fix16 product for 8080/8085/gbz80).

+ 11. Specials stay off the finite path. Classify Inf/NaN on overflow / zero / equal-exp 255 (packed exp 31) only. `inc r` / `jp Z` tests exp==255 (8-bit inc sets Z, not C). Pack underflow is unsigned `jp C` after `sub 112` (not `jp M`: d=255 → 143 looks minus). Packed Inf × tiny finite (sum−15 < 31) may not be Inf.

+ 12. gbz80: no cheap `ex (sp),hl` (148c helper). Open-code: park DE, `ld hl,sp+n`, swap through `(hl)`, restore DE; **BC is often the return**. No `jp P` / `ret m` (no S): `bit 7,h`.

+ 13. MPL v2 panel on **`asm/`** cores only — not `c/` glue, lm16 aliases, or C (some C is GPL).

+ 14. Restoring f24 div: z80 uses `exx` + `djnz` (count in `B'`). 8085 / 8080 / gbz80 have no spare count register (B is the divisor). After prenorm, DE is free: **stacked ret** — push `div_pack`, 15× `div_bit`, `jp div_bit`; `div_bit` ends in `ret`. Do **not** `call div_bit` 16 times. 8080/gbz80 inner `push de`/`push af` sit above those words. z80 keeps the `djnz` loop.