math, crypto, hash: Write power64 versions of assembler routines where applicable

[ianlancetaylor]

We want to write power64 versions of the assembler routines in the math package, in
several crypto packages, and in the hash/crc32 package.  For each of those packages
where we have .s files, we should either write a power64 version or determine that the
Go version is as good as we can write in assembler.

[minux]

Comment 1:

power8 has a lot of specific instructions for those kinds of things, i think hand
written assembly will definitely beat the generic version.
I assume you also mean math/big.

[minux]

Comment 2:

also, there are some functions that belong to bytes and strings packages but reside in
the runtime package (e.g. bytes.Equal, bytes.IndexByte, etc.)
the memcmp and memclr in the runtime package also need to be rewritten.

[minux]

Comment 3:

also, there are some functions that belong to bytes and strings packages but reside in
the runtime package (e.g. bytes.Equal, bytes.IndexByte, etc.)
the memcmp and memclr in the runtime package also need to be rewritten.

[ianlancetaylor]

Comment 4:

This is specifically:
crypto/md5/md5block_power64x.s
crypto/rc4/rc4_power64x.s
crypto/sha1/sha1block_power64x.s
crypto/sha256/sha256block_power64x.s
crypto/sha512/sha512block_power64x.s
hash/crc32/crc32_power64x.s
math/abs_power64x.s
math/asin_power64x.s
math/atan2_power64x.s
math/atan_power64x.s
math/dim_power64x.s
math/exp2_power64x.s
math/exp_power64x.s
math/expm1_power64x.s
math/floor_power64x.s
math/frexp_power64x.s
math/hypot_power64x.s
math/ldexp_power64x.s
math/log10_power64x.s
math/log1p_power64x.s
math/low_power64x.s
math/mod_power64x.s
math/modf_power64x.s
math/remainder_power64x.s
math/sin_power64x.s
math/sincos_power64x.s
math/sqrt_power64x.s
math/tan_power64x.s
math/big/arith_power64x.s
reflect/asm_power64x.s
runtime/memclr_power64x.s
runtime/memmove_power64x.s
Several of the math files are likely to be trivial, simply jumps to the Go code.