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Merge #19403: build: improve __builtin_clz* detection

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9952242c03 build: improve builtin_clz* detection (fanquake)

Pull request description:

  Fixes #19402.

  The way we currently test for `__builtin_clz*` support with `AC_CHECK_DECLS` does not work with Clang:
  ```bash
  configure:21492: clang++-10 -std=c++11 -c -g -O2  -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS conftest.cpp >&5
  conftest.cpp:100:10: error: builtin functions must be directly called
    (void) __builtin_clz;
           ^
  1 error generated.
  ```

  This also removes the `__builtin_clz()` check, as we don't actually use it anywhere, and it's trvial to re-add detection if we do start using it at some point. If this is controversial then I'll add a test for it as well.

ACKs for top commit:
  sipa:
    ACK 9952242c03
  laanwj:
    ACK 9952242c03

Tree-SHA512: 695abb1a694a01a25aaa483b4fffa7d598842f2ba4fe8630fbed9ce5450b915c33bf34bb16ad16a16b702dd7c91ebf49fe509a2498b9e28254fe0ec5177bbac0
This commit is contained in:
Wladimir J. van der Laan
2020-06-29 15:49:04 +02:00
parent 8edfc1715a 9952242c03
commit 1269cab21a
3 changed files with 17 additions and 15 deletions
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4
src/crypto/common.h
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@@ -82,12 +82,12 @@ void static inline WriteBE64(unsigned char* ptr, uint64_t x)
/** Return the smallest number n such that (x >> n) == 0 (or 64 if the highest bit in x is set. */
uint64_t static inline CountBits(uint64_t x)
{
#if HAVE_DECL___BUILTIN_CLZL
#if HAVE_BUILTIN_CLZL
if (sizeof(unsigned long) >= sizeof(uint64_t)) {
return x ? 8 * sizeof(unsigned long) - __builtin_clzl(x) : 0;
}
#endif
#if HAVE_DECL___BUILTIN_CLZLL
#if HAVE_BUILTIN_CLZLL
if (sizeof(unsigned long long) >= sizeof(uint64_t)) {
return x ? 8 * sizeof(unsigned long long) - __builtin_clzll(x) : 0;
}