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Migrate feature detection macro checks from #ifdef to #if.

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The #if predicate evaluates to false if the macro is undefined, or
defined to 0. #ifdef (and its synonym #if defined) evaluates to false
only if the macro is undefined.

The new setup allows differentiating between setting a macro to 0 (to
express that the capability definitely does not exist / should not be
used) and leaving a macro undefined (to express not knowing whether a
capability exists / not caring if a capability is used).

PiperOrigin-RevId: 391094241
This commit is contained in:
Victor Costan
2021-08-16 18:22:31 +00:00
committed by Victor Costan
parent a8400f1fab
commit cbb83a1d64
7 changed files with 44 additions and 43 deletions
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4
snappy_test_tool.cc
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@@ -66,7 +66,7 @@ namespace snappy {
namespace {
#if defined(HAVE_FUNC_MMAP) && defined(HAVE_FUNC_SYSCONF)
#if HAVE_FUNC_MMAP && HAVE_FUNC_SYSCONF
// To test against code that reads beyond its input, this class copies a
// string to a newly allocated group of pages, the last of which
@@ -112,7 +112,7 @@ class DataEndingAtUnreadablePage {
size_t size_;
};
#else // defined(HAVE_FUNC_MMAP) && defined(HAVE_FUNC_SYSCONF)
#else // HAVE_FUNC_MMAP && HAVE_FUNC_SYSCONF
// Fallback for systems without mmap.
using DataEndingAtUnreadablePage = std::string;