Every measurement repeats until a stated interval has passed, so a clock
that reads the same value twice does not slow the benchmark down, it stops
it returning at all.
CLOCK_MONOTONIC does not advance on every target. On qemu-intel64 it
reports success and stays at zero, while CLOCK_REALTIME advances normally,
and the benchmark spins in its first measurement with no output after the
heading.
Sample each candidate twice around a busy wait and take the first one whose
reading changes. Where none does, say so and skip the timing rather than
hang.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
Neither is covered here, and both are overridable, so a machine or libc
implementation of either goes in unmeasured and unchecked.
memccpy is checked with the search character present, where the copy
stops just past it and the result points there, and absent, where the
whole length is copied and the result is NULL. stpncpy is checked
against every capacity from zero to four past the length, for the
content, the zero padding beyond the terminator, and the returned
pointer, which is the terminator when the string fits and one past the
end when it does not.
Both sweep all sixty four source and destination alignment pairs, and
both are added to the benchmark, which now covers nineteen functions.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
The existing speed checks time one call at one size, 128 bytes, with both
operands aligned. A machine implementation usually takes its wide path
only when the pointers satisfy some alignment condition, so that single
point reports the best case and says nothing about the rest of the input
space.
Measure the same functions across a size sweep and every source and
destination alignment pair instead, plus strlcpy. On rv64 the difference
this exposes is not marginal:
strcpy 32768 B s+0/d+0 2938.0 MB/s
strcpy 32768 B s+1/d+1 2942.0 MB/s
strcpy 32768 B s+1/d+2 626.0 MB/s
memcmp 32768 B s+0/d+0 412.4 MB/s
memcmp 32768 B s+1/d+2 41.0 MB/s
Two pointers misaligned by the same amount run at the aligned rate;
misaligned by different amounts they fall to a tenth of it. Neither
number is visible from an aligned measurement alone.
A function with no machine implementation reports the same rate at every
alignment, so the sweep also shows which of them a machine directory
actually covers.
Each result reports MB/s, which compares across machines, and cycles per
byte where perf_gettime() is reachable from an application, both from one
timed loop. strcat starts from an empty destination on each turn, since
appending to the last result would grow it without bound, so its figure
includes that store.
It sits behind TESTING_ARCH_LIBC_BENCH, default n, because a measurement
runs for a fixed interval and a full sweep takes about a minute.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
