This function causes problems with gcc 5 which incorrectly complains
about the call to warn_if inside a constexpr function. That should only
be an error if a call to a non-constexpr is unavoidable, and even then
the compiler isn't required to emit a diagnostic.
Rather than drop the warning, or add ifdefs to deal with these defective
versions of gcc, this change eliminates the power() function entirely.
Most inputs to this function would overflow anyway, which is reportedly
why no integer version of an exponentiation function is defined in the
standard library, and all uses of this function can easily and more
efficiently be replaced by simple left and right shifts.
Finally, by eliminating the power() function, we also remove the
dependence on base/logging.hh.
Change-Id: I4d014163883d12db46da4ee752696c8225534ee8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42504
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
As described in the Jira issue, this replaces the implementation of
isPowerOf2() and power(). It also revamps floorLog2 so that there only
needs to be one implementation and no assumptions about how big certain
types are.
The way power() used to work was to raise a number n to an exponent e
by multiplying n times itself e times. As a warning in this function
explains, this can be quite slow for large e. A much more efficient
way to raise a number to an exponent is to square n over and over, and
to multiply in the current square if that bit of e is set.
n ^ 15 = (n^1) * (n^2) * (n^4) * (n^8)
n^8 = (n^4)^2
n^4 = (n^2)^2
n^2 = n^2
n^1 = n
So that takes 6 multiplications, n^2, (n^2)^2, (n^4)^2, and then each
multipy to compute the final result, instead of 14.
The difference is more pronounced for larger exponents, although you'd
quickly start to overflow a uint64_t.
Jira Issue: https://gem5.atlassian.net/browse/GEM5-140
Change-Id: I0ae05aeba1b5882d2a616613b1679e6206b4cbfe
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26164
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Testing intmath.hh and intmath.cc. Here is the
list of the functions that are tested.
intmath.isPowerOf2, intmath.power, intmath.floorLog2,
intmath.ceilLog2, intmath.divCeil, intmath.roundUp,
intmath.roundDown. Other functions are not tested,
because they are not currently used and are dead code.
Change-Id: I150ac1b5cead93c6698a8c9e9cec80bd87ef181a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22081
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Mahyar Samani <msamani@ucdavis.edu>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
