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https://github.com/gbdev/rgbds.git
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116 lines
2.5 KiB
C++
116 lines
2.5 KiB
C++
// SPDX-License-Identifier: MIT
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#ifndef RGBDS_HELPERS_HPP
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#define RGBDS_HELPERS_HPP
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// Ideally we'd use `std::unreachable`, but it has insufficient compiler support
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#ifdef __GNUC__ // GCC or compatible
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#ifdef NDEBUG
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#define unreachable_ __builtin_unreachable
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#else
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// In release builds, define "unreachable" as such, but trap in debug builds
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#define unreachable_ __builtin_trap
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#endif
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#else
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// This seems to generate similar code to __builtin_unreachable, despite different semantics
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// Note that executing this is undefined behavior (declared [[noreturn]], but does return)
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[[noreturn]]
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static inline void unreachable_() {
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}
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#endif
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// Ideally we'd use `[[assume()]]`, but it has insufficient compiler support
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#ifdef NDEBUG
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#ifdef _MSC_VER
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#define assume(x) __assume(x)
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#else
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// `[[gnu::assume()]]` for GCC or compatible also has insufficient support (GCC 13+ only)
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#define assume(x) \
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do { \
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if (!(x)) { \
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unreachable_(); \
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} \
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} while (0)
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#endif
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#else
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// In release builds, define "assume" as such, but `assert` in debug builds
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#include <assert.h>
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#define assume assert
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#endif
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// Ideally we'd use `std::bit_width`, but it has insufficient compiler support
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#ifdef __GNUC__ // GCC or compatible
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#define ctz __builtin_ctz
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#define clz __builtin_clz
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#elif defined(_MSC_VER)
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#include <intrin.h>
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#pragma intrinsic(_BitScanReverse, _BitScanForward)
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static inline int ctz(unsigned int x) {
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unsigned long cnt;
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assume(x != 0);
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_BitScanForward(&cnt, x);
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return cnt;
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}
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static inline int clz(unsigned int x) {
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unsigned long cnt;
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assume(x != 0);
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_BitScanReverse(&cnt, x);
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return 31 - cnt;
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}
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#else
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#include <limits.h>
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static inline int ctz(unsigned int x) {
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int cnt = 0;
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while (!(x & 1)) {
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x >>= 1;
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++cnt;
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}
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return cnt;
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}
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static inline int clz(unsigned int x) {
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int cnt = 0;
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while (x <= UINT_MAX / 2) {
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x <<= 1;
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++cnt;
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}
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return cnt;
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}
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#endif
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// Macros for stringification
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#define STR(x) #x
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#define EXPAND_AND_STR(x) STR(x)
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// Macros for concatenation
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#define CAT(x, y) x##y
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#define EXPAND_AND_CAT(x, y) CAT(x, y)
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// For lack of <ranges>, this adds some more brevity
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#define RANGE(s) std::begin(s), std::end(s)
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// MSVC does not inline `strlen()` or `.length()` of a constant string
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template<int N>
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static constexpr int literal_strlen(char const (&)[N]) {
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return N - 1;
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}
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// For ad-hoc RAII in place of a `defer` statement or cross-platform `__attribute__((cleanup))`
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template<typename T>
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struct Defer {
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T deferred;
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Defer(T func) : deferred(func) {}
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~Defer() { deferred(); }
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};
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#endif // RGBDS_HELPERS_HPP
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