`log2` instrinsic

[brandongc]

Currently the standard has log and log10 functions, but no log2.

[milancurcic]

Good candidate for stdlib.

[brandongc]

or more generally, parity with math.h from C

[gklimowicz]

or more generally, parity with math.h from C

After a brief discussion of this in JoR (Journal of Requirements) at the WG5 meeting this week, if there is a strong use case for this, please make it.

In general, feature parity with C math.h (in and of itself) doesn't appear to be a high priority for Fortran standards committee.

The best way to get this moved on to the "We really should do it" list is to make a strong use case for it ho help justify the return on investment for implementers.

[klausler]

It's not about feature parity with C, it's about feature parity with the modern IEEE-754 standard for floating-point arithmetic. log2 is one member of its list of recommended functions, and Fortran already has most of the rest.

[gklimowicz]

The best way to get this moved on to the "We really should do it" list is to make a strong use case for it ho help justify the return on investment for implementers.

Peter's argument works for me, too. I'll see what I can do to help move this forward.

[brandongc]

From Table 9.1 from IEEE-754

• exp
• expm1
• exp2
• exp2m1
• exp10
• exp10m1
• log
• log2
• log10
• logp1
• log2p1
• log10p1
• hypot
• rSqrt
• compound
• rootn
• pown
• sin
• cos
• tan
• sinPi
• cosPi
• tanPi
• asin
• acos
• atan
• atan2
• sinh
• cosh
• tanh
• acosh
• atanh