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Avoid >> above type width in BitWriter #74

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Merged
merged 2 commits into from
Apr 11, 2024
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Avoid >> above type width in BitWriter #74

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154bcd4
Avoid >> above type width in BitWriter
sipa Oct 19, 2022
fe1040f
Drop -Wno-shift-count-overflow compile flag
sipa Oct 19, 2022
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5 changes: 0 additions & 5 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -104,11 +104,6 @@ esac
AX_CHECK_COMPILE_FLAG([-Wall],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wall"],,[[$CXXFLAG_WERROR]])
AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[CXXFLAGS="$CXXFLAGS -fvisibility=hidden"],[],[$CXXFLAG_WERROR])

## Some compilers (gcc) ignore unknown -Wno-* options, but warn about all
## unknown options if any other warning is produced. Test the -Wfoo case, and
## set the -Wno-foo case if it works.
AX_CHECK_COMPILE_FLAG([-Wshift-count-overflow],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-shift-count-overflow"],,[[$CXXFLAG_WERROR]])

if test "x$use_ccache" != "xno"; then
AC_MSG_CHECKING(if ccache should be used)
if test x$CCACHE = x; then
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20 changes: 16 additions & 4 deletions src/int_utils.h
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Expand Up @@ -55,11 +55,10 @@ class BitWriter {
int offset = 0;
unsigned char* out;

public:
BitWriter(unsigned char* output) : out(output) {}

template<int BITS, typename I>
inline void Write(I val) {
inline void WriteInner(I val) {
// We right shift by up to 8 bits below. Verify that's well defined for the type I.
static_assert(std::numeric_limits<I>::digits > 8, "BitWriter::WriteInner needs I > 8 bits");
int bits = BITS;
if (bits + offset >= 8) {
state |= ((val & ((I(1) << (8 - offset)) - 1)) << offset);
Expand All @@ -78,6 +77,19 @@ class BitWriter {
offset += bits;
}


public:
BitWriter(unsigned char* output) : out(output) {}

template<int BITS, typename I>
inline void Write(I val) {
Comment on lines +84 to +85
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@hebasto hebasto Oct 19, 2022

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Whether inline makes anything for templates?

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@sipa sipa Oct 19, 2022

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inline has two meanings in C++:

  • A semantic one, permitting multiple identical definitions in separate translation units.
  • A hint for the compiler that inlining the function is desired.

The first one is always true for templated things, but the second one isn't.

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@hebasto hebasto Oct 19, 2022

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  • A hint for the compiler that inlining the function is desired.

I thought that C++ standard abandoned this meaning of the inline keyword, especially since C++17.

https://en.cppreference.com/w/cpp/language/inline

Of course, compilers could have different opinions :)

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@sipa sipa Oct 19, 2022

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I think you're misreading that page. The C++17 specific boxes explain that variables can be inline too now, justified by the fact that inline has ended up meaning "multiple definitions are allowed". It doesn't say anything about whether compilers do or don't also take inline into account for making inlining decisions (which isn't possible anyway, as there is no observable effect from the perspective of language definition).

// If I is smaller than an unsigned int, invoke WriteInner with argument converted to unsigned.
using compute_type = typename std::conditional<
(std::numeric_limits<I>::digits < std::numeric_limits<unsigned>::digits),
unsigned, I>::type;
return WriteInner<BITS, compute_type>(val);
}

inline void Flush() {
if (offset) {
*(out++) = state;
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