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bitset: optimize the code generated by shifts in common cases

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* spot/misc/bitset.hh: Here.
* spot/misc/bitset.cc: New file.
* spot/misc/Makefile.am: Add it.
* spot/twa/acc.hh: Conditionally remove the exception checks around
shift operators.
* spot/misc/common.hh (SPOT_ASSUME): New macro.
This commit is contained in:
Alexandre Duret-Lutz 2018-05-24 17:20:16 +02:00
parent e979791071
commit cc2c4615d0
5 changed files with 118 additions and 55 deletions
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75
spot/misc/bitset.hh
View file

@ -25,6 +25,13 @@
namespace spot
{
#ifndef SWIG
namespace internal
{
[[noreturn]] SPOT_API void report_bit_shift_too_big();
}
#endif
template<size_t N>
class bitset
{
@ -37,14 +44,13 @@ namespace spot
/// a special constructor for -1 (cf. mone below)
struct minus_one_tag {};
explicit bitset(minus_one_tag)
: data{0}
{
for (auto& v : data)
v -= 1;
v = -1U;
}
constexpr explicit bitset(word_t s)
: data{s}
: data{{s}}
{
SPOT_ASSERT(s == 0U || s == 1U);
}
@ -133,23 +139,36 @@ namespace spot
bitset& operator<<=(unsigned s)
{
if (SPOT_UNLIKELY(s >= 8*N*sizeof(word_t)))
throw std::runtime_error("bit shift overflow is undefined behavior");
#if SPOT_DEBUG || SWIG
if (SPOT_UNLIKELY(s >= 8 * N * sizeof(word_t)))
internal::report_bit_shift_too_big();
#else
SPOT_ASSUME(s < 8 * N * sizeof(word_t));
#endif
// Skip the rest of this function in the most common case of
// N==1. g++ 6 can optimize away all the loops if N==1, but
// clang++4 cannot and needs help.
if (N == 1)
{
data[0] <<= s;
return *this;
}
if (s == 0)
return *this;
const unsigned wshift = s / (8*sizeof(word_t));
const unsigned offset = s % (8*sizeof(word_t));
const unsigned wshift = s / (8 * sizeof(word_t));
const unsigned offset = s % (8 * sizeof(word_t));
if (offset == 0)
{
for (unsigned i = N-1; i >= wshift; --i)
data[i] = data[i - wshift];
}
{
for (unsigned i = N - 1; i >= wshift; --i)
data[i] = data[i - wshift];
}
else
{
const unsigned sub_offset = 8*sizeof(word_t) - offset;
for (unsigned i = N-1; i > wshift; --i)
const unsigned sub_offset = 8 * sizeof(word_t) - offset;
for (unsigned i = N - 1; i > wshift; --i)
data[i] = ((data[i - wshift] << offset) |
(data[i - wshift - 1] >> sub_offset));
data[wshift] = data[0] << offset;
@ -160,25 +179,39 @@ namespace spot
bitset& operator>>=(unsigned s)
{
if (SPOT_UNLIKELY(s >= 8*N*sizeof(word_t)))
throw std::runtime_error("bit shift overflow is undefined behavior");
#if SPOT_DEBUG || SWIG
if (SPOT_UNLIKELY(s >= 8 * N * sizeof(word_t)))
internal::report_bit_shift_too_big();
#else
SPOT_ASSUME(s < 8 * N * sizeof(word_t));
#endif
// Skip the rest of this function in the most common case of
// N==1. g++ 6 can optimize away all the loops if N==1, but
// clang++4 cannot and needs help.
if (N == 1)
{
data[0] >>= s;
return *this;
}
if (s == 0)
return *this;
const unsigned wshift = s / (8*sizeof(word_t));
const unsigned offset = s % (8*sizeof(word_t));
const unsigned wshift = s / (8 * sizeof(word_t));
const unsigned offset = s % (8 * sizeof(word_t));
const unsigned limit = N - wshift - 1;
if (offset == 0)
for (unsigned i = 0; i <= limit; ++i)
data[i] = data[i + wshift];
{
for (unsigned i = 0; i <= limit; ++i)
data[i] = data[i + wshift];
}
else
{
const unsigned sub_offset = 8*sizeof(word_t) - offset;
const unsigned sub_offset = 8 * sizeof(word_t) - offset;
for (unsigned i = 0; i < limit; ++i)
data[i] = ((data[i + wshift] >> offset) |
(data[i + wshift + 1] << sub_offset));
data[limit] = data[N-1] >> offset;
data[limit] = data[N - 1] >> offset;
}
std::fill(data.begin() + limit + 1, data.end(), word_t(0));
return *this;