fix(libc): integrate current main and log10 parent into log2

docs/dev/debt/libc.md

@@ -151,6 +151,7 @@
 - [nextafter and nextafterf](../../../core/libs/prx/libc/src/Math.cpp) (libc) have no physical-console or unmasked-exception validation. A Linux CPU probe compares result bits, `errno` and masked floating-point flags with the unchanged math code in FAR: Changing Tides PPSA03766 bundled `libc.prx` (`nextafter` 0x51b30, `nextafterf` 0x51c80, `_Feraise` 0x11da0): 16,864 calls across both precisions, four rounding modes and all DAZ/FTZ combinations, not exhaustive inputs. Earlier Windows sampling of eleven bundled libraries compares only bits and `errno`; exception behavior outside the FAR module remains unverified.
 - [tanh](../../../core/libs/prx/libc/src/Math.cpp) (libc) does not compare floating-point exceptions, and its double inputs are checked by sampling, not exhaustively. It is FreeBSD msun's [`s_tanh.c`](https://github.com/freebsd/freebsd-src/blob/release/11.4.0/lib/msun/src/s_tanh.c) over this file's msun `Expm1`, with `tiny` read at run time; it sets no `errno`, as the titles' `libc.prx` does not. It gives the same bits as the `tanh` bundled with PPSA07923 and PPSA05916 on 16 million random and 68,211 structured arguments on a Windows host; the FMA-contracted build bundled with PPSA13934 differs on 1,054 of them.
 - [log10](../../../core/libs/prx/libc/src/Math.cpp) (libc) does not compare floating-point exceptions, and its double inputs are checked by sampling, not exhaustively. It is the fdlibm [`e_log10.c`](https://github.com/freebsd/freebsd-src/blob/59bc2f095289a10b8cfa55cbb2b45c3bd6c2d4ae/lib/msun/src/e_log10.c) over its [`k_log.h`](https://github.com/freebsd/freebsd-src/blob/59bc2f095289a10b8cfa55cbb2b45c3bd6c2d4ae/lib/msun/src/k_log.h), which FreeBSD 11.4 later replaced. As the titles' `libc.prx` does, it sets `EDOM` for every nonzero argument with the sign bit set (negatives, `-inf` and negative NaNs) and leaves `errno` alone for ±0, where it returns `-inf`, unlike `log`. It gives the same bits, NaN payloads included, and `errno` as the `log10` bundled with PPSA07923 and PPSA05916 on 320 million random and 31,165 structured arguments on a Windows host. The FMA-contracted build bundled with PPSA13934 differs on 229,944 of the random ones.
+- [log2](../../../core/libs/prx/libc/src/Math.cpp) (libc) does not compare floating-point exceptions, and its double inputs are checked by sampling, not exhaustively. It is the fdlibm [`e_log2.c`](https://github.com/freebsd/freebsd-src/blob/59bc2f095289a10b8cfa55cbb2b45c3bd6c2d4ae/lib/msun/src/e_log2.c) over the same `k_log.h` kernel as `log10` (`KernelLog`), which FreeBSD 11.4 later replaced. As the titles' `libc.prx` does, it sets `EDOM` for every nonzero argument with the sign bit set and leaves `errno` alone for ±0. It gives the same bits, NaN payloads included, and `errno` as the `log2` bundled with PPSA07923 and PPSA05916 on 16 million random and 31,165 structured arguments on a Windows host; the FMA-contracted build bundled with PPSA13934 differs on 727 of the random ones.
 - [sinhf](../../../core/libs/prx/libc/src/Math.cpp) (libc) follows the `sinhf` of the `libc.prx` bundled with PPSA28319 (disassembly): FreeBSD msun's [`e_sinhf.c`](https://github.com/freebsd/freebsd-src/blob/5aa554c7e5b6fd9042986df07f12ac5687e41392/lib/msun/src/e_sinhf.c) from before `__ldexp_expf`, which squares `expf(|x| / 2)` between `logf(FLT_MAX)` and the overflow threshold, calling msun's [`expm1f`](https://github.com/freebsd/freebsd-src/blob/59bc2f095289a10b8cfa55cbb2b45c3bd6c2d4ae/lib/msun/src/s_expm1f.c) and [`expf`](https://github.com/freebsd/freebsd-src/blob/59bc2f095289a10b8cfa55cbb2b45c3bd6c2d4ae/lib/msun/src/e_expf.c), whose paths for the arguments it passes are inlined here. Past the threshold Sony's error helper sets `errno` to `ERANGE` before returning `x * 1e37`; msun itself sets no `errno`. That code, run on a Windows host, gives the same bits as this implementation for every finite argument up to the threshold, of both signs; it was not run on Linux. That the system `libSceLibcInternal`, which Ruffle (PPSA68091) and RetroArch (PPSA99169) import while bundling a zero-return `libc.prx`, has the same code is assumed
 - [acoshf](../../../core/libs/prx/libc/src/Math.cpp) (libc) exact system `libSceLibcInternal` behavior and FMA-contracted copies remain unverified. Positive finite inputs use [msun](https://github.com/freebsd/freebsd-src/blob/5aa554c7e5b6fd9042986df07f12ac5687e41392/lib/msun/src/e_acoshf.c) range handling and this file's `logf`; the middle range divides -1 before addition under directed rounding. Bits, errno and SSE/x87 status and controls match the supplied PPSA03766/PPSA07923 copies on 236,592 positive finite calls (4,929 inputs, four rounding modes, DAZ/FTZ combinations and sticky flags); these samples are not exhaustive. Invalid-domain errno and SSE/x87 invalid flags are checked against two supplied bundled copies; those samples are not exhaustive either.
 - [acoshl, asinhl, atanhl, atan2l, cbrtl, erfl, erfcl, expm1l, hypotl, log1pl, log2l, lgammal, tgammal, j0f, j1f, jnf, y0f, y1f and ynf](../../../core/libs/prx/libc/src/Math.cpp) (libc) return the host C library's results (the float Bessel functions through its double ones), not those of the console's own code, so the last bits can differ (`y0f`, `y1f`, `ynf` follow the console at `+-0`). `tgammaf` delegates to the host's double `tgamma` as FreeBSD 11 does ([`s_tgammaf.c`](https://github.com/freebsd/freebsd-src/blob/stable/11/lib/msun/src/s_tgammaf.c)), then restores the sign of a zero result for negative non-integer inputs from the parity of `floor(-x)`; nine title-bundled `libc.prx` builds return that sign for underflowing inputs, where Windows UCRT can return the opposite sign ([#9707](https://github.com/boykopovar/AnyPS5/issues/9707)). As in the console's `libSceLibcInternal.sprx` (SDK 4.5x build of `J03950001`, 0x56410), `lgammal` does not store the sign in `signgam`; `hypotl` returns infinity for an infinite argument even when the other is a NaN, as C11 F.10.4.3 requires. [hypot3, hypot3f and hypot3l](../../../core/libs/prx/libc/src/Math.cpp) follow that module (0x51D30, 0x520D0, 0x52420): the first NaN of x, y and z is returned unchanged, any infinity gives positive infinity, a zero argument gives the two-argument hypot of the other two, and otherwise the largest magnitude is combined with the hypot of the other two