skip CONSTP(dmax) CONSTP(slen) as they prohibit constant folding
of this expr.
TODO: always_inline helps in arg propagation (-O3),
but needs to be probed for.

no _real, static inline _unchecked worker, and
2 exported funcs: _s (already checked) and _s_chk (some unchecked,
deferred to run-time checks)

See #48

skip run-time checks when already checked at compile-time.
split functions into two: unchecked and checked, depending
on the already done compile-time check.

currently only useful for clang-5+
gcc cannot not handle BOS as compile-time constant, how lame.

shaves off 10% p_memcpy_s, when all 4 args are of known size + constant len.
See #48

Probe for static_assert in CXX11 or C11

If args are compile-time constants and satisfy a constant expr,
call the func, otherwise produce a compile-time error.
But static_assert cannot be used inside args, only as statement.

See #48

to avoid downloading it

from config.h
They are needed by the library users in safe_compile.h for
compile-time checks.
HAVE___BUILTIN_CONSTANT_P, HAVE_WARN_DMAX, HAVE_ERROR_DMAX

overflow checks are not reliable on linux yet

only detected with clang-5 -O2, which doesnt clear the static str1
and reuses the word after. not even valgrind detected that overflow.
add to smoke.sh

similar to memcpy_s, just that gcc is doing ok here.

use 64bit copy on 64bit machines, not just 32bit.
memcpy_s is now as fast as memcpy native, with in overhead
of -1 to +3%, on clang-4+
gcc is only 77% slower, not 89%.

esp. memcpy_s is significantly faster with
clang-7 on darwin. Only 50-55% slowdown, not 90%.
And with clang-4+ -march=native the overhead is only 5-20%.

there is no measurable --disable-constraint-handler speedup,
but a huge _s slowdown of ~90%.
The size overhead for the constraint-handler is 35%-100%.

Use proper timings, asm rdtsc

undef the run-time invoke_safe_{str,mem}_constraint_handler function calls
in safe_config.h to avoid the large errormsg strings.  As in freebsd.

Most of the OS/libc folks complain about it, but it is useful, similar to
the malloc hooks.  They are only used in the error cases.

Closes #50

destbos is -1 then. no clearing in this case.
only detected on glibc/gcc-7 with -Werror=stringop-overflow
specified size 18446744073709551612 exceeds maximum object size 9223372036854775807

Closes #40.

Todo: Now the msvcrt checks can be switched back to compile-time,
and #ifdef's.

and clear dest on EOVERFLOW and ESNOSPC

Cast pointers to be compared to (uintptr_t) as in mem_prim_move
"Comparing pointers from two separately allocated objects is forbidden as
per 6.5.8 C11 except when using (in)equality."

See also intel/safestringlib#18
Closes GH #51

needs to be supressed.
bsd allocates a fresh struct tm in a helper thread for _r,
which needs to be supressed. it is with glibc.

without tests yet

dont apply the early slen check optimization from strstr yet

and pass the ptr arg to the constraint handler

to link to the native functions, not _chk

convert to _chk, check for dest overflows.

remove errno, return negative error codes, as with s{n}printf_s.

ESUNTERM for src to avoid overflows.

overload checks with const literal strings fail on travis with clang-5.0 on
linux