add TODO list

[libm] / TODO

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+ldhack.h fix:
+       move ldouble manipulation into arch specific headers
+long double isnan, isinf..:
+       efficient macro versions of long double classification macros?
+       (they are ld* representation specific)
+lrint:
+       does inexact allowed on overflow?
+       see c99 7.12, 7.12.9.5, F.9, F.9.6.5
+small file cleanups:
+       if libm.h internals is not needed (ldexp,..) then include math.h only
+       LD64 wrap small long double functions as well
+trigonometric functions:
+       __rem_pio_large: is returning 2 bits enough?
+       __tan: 3rd arg semantics is probably not optimal
+       sinf,cosf: return sindf(-y) vs -sindf(y)?
+       __sin,__cos,..: z,w,.. -> x2,x4,.. so degree is easier to see
+       __rem_pio2*: rounding trick: simply use the low 32 bits of fn?
+nan:
+       use strtod? c99 7.12.11.2
+scalbf:
+       scalb is buggy, do we need the *f and *l version?
+scalbn:
+       needs a rewrite: signed int problems, wrong <-50000 check
+__ldexp_cexp:
+       only complex in math/, move to cmath?
+j0l, y0l,..:
+       declare long double bessel functions in math.h?
+uniform inexact exception raising:
+       (int)x == 0 and huge+x > 0 are used
+       unreachable code is not commented and hard to follow
+generic code fixes:
+       int32_t -> uint32_t conversion (subtle)
+       += 1, -= 1 -> ++, --
+       TWO52, one, zero, twom1000,.. -> use reasonable consts
+       (float)1 -> 1.0f
+       ldexp -> use scalbn internally (ldexp is a wrapper)
+       i386 vs precision -> assume extended prec setting
+       long double const trunc/slowness bug
+       remove "unsupported long double format" checks
+       sign bit (sqrt)
+fma:
+       expects single 53bit rounding
+       rewrite using long double arithmetics?
+log2:
+       dekker vs long double arithmetics
+tgamma:
+       missing
+       lanczos approx as in boost/math/special_functions, python/Modules/mathmodule.c
+       or bsd tgamma
+complex
+       optimizable creal cimag (libm.h macro for internal code?)
+       test? (using mdc lib, available test vectors,..)
+       Kahan, W. "Branch Cuts for Complex Elementary Functions, or Much Ado About Nothing's Sign Bit." 1987
+       Hull, Fairgrieve, Tang "Implementing complex elementary functions using exception handling" 1994
+       Hull, Fairgrieve, Tang "Implementing the complex arcsine and arccosine functions using exception handling" 1997
+       boost/math/complex
+       python/Modules/cmathmodule.c (+math, cmath tests)
+asm:
+       i386, x86_64 asm versions
+libm test
+       test vectors
+       special cases from c99 F.9, G
+       randomized test using mpfr
+arm fenv?