CppCon 2024: Improving our safety with a quantities and units library C++ developers needs help 8• Aerospace • Autonomous cars • Embedded industries CppCon 2024: Improving our safety with a quantities dimension T-1 angular_velocity\n(angular_displacement / duration)\n[rad/s, 1/s]\n{vector} frequency\n(1 / period_duration)\n[Hz, 1/s] rotational_frequency\n(rotation / duration)\n[1/s] angular_frequency\n(phase_angle mp_units::si { inline constexpr struct radian final : named_unit<"rad", metre / metre, kind_ofangular_measure>> {} radian; inline constexpr struct steradian final : named_unit<"sr", square(metre) / square(metre)

Intra-register sorting • Fast linear median-of-seven filter • Fast small-kernel convolution • Faster (?) UTF-8 to UTF-32 conversion (with AVX2) • No heavy code, but lots of pictures • Thinking "vertically" CppCon 2020 Bob Steagall K E W B C O M P U T I N G Convolution CppCon 2020 - Adventures in SIMD Thinking 8 S = s0 s1 s2 s3 s4 s5 s6 ... K = k0 k1 k2 r0 = ... r1 = s0k0 + s6 s7 s8 k1 k1 k1 k1 k1 k1 k1 k1 s2 s3 s4 s5 s6 s7 s8 s9 k2 k2 k2 k2 k2 k2 k2 k2 r1 r2 r3 r4 r5 r6 r7 r8Copyright © 2020

RAII •Beyond basic lifetime •Common pitfalls •Value categories •Unions/Arrays •Any assembly code 8 On this talk…• Principal Software Engineer @ Cadence Design Systems • Learning C++ since 2013 • Can’t olt.org/z/ffzG8hPT8 struct Foo { Foo() { std::cout << "Foo()" << std::endl; } ~Foo() { std::cout << "~Foo()" << std::endl; } }; int main() { Foo a; { Foo b; } } 1 2 3 4 5 6 7 8 9 10 11 21 Constructors olt.org/z/ffzG8hPT8 struct Foo { Foo() { std::cout << "Foo()" << std::endl; } ~Foo() { std::cout << "~Foo()" << std::endl; } }; int main() { Foo a; { Foo b; } } 1 2 3 4 5 6 7 8 9 10 11 22 Constructors

operation that’s not too boring, say matrix addition 6Back to high school 7Back to high school 8Back to C++ If the matrices are contiguous in memory, then we can treat them as ranges and simply use rhsRowStride, 5 float* dst, size_t dstRowStride 6 ) { 7 for (size_t i = 0; i < rows; ++i) 8 for (size_t j = 0; j < cols; ++j) 9 dst[dstRowStride * i + j] = 10 j]; 12 } 12add r10, r11 add r9, r8 cmp rcx, rdi je .LBB0_16 .LBB0_3: test rsi, rsi je .LBB0_2 cmp rsi, 8 jb .LBB0_11 mov r11, rbx

“people are not writing enough functions” 7Tony Van Eerd: “people are not writing enough functions” 8When people finally start writing more functions, we’d prefer to get only the well designed ones!When System V gABI psABI: ARM, x86, … C++ Itanium ABI Microsoft Windows ABIs C++ Standard 18armv8-a System V ABI - iPhone - M1 Mac and newer - Android smartphone x86-64 (AMD64) System V ABI - Linux x86 (IA-32) Microsoft ABI - ancient Windows device 19armv8-a System V ABI Procedure Call Standard for the Arm® 64-bit Architecture armv8-a clang 18.1.0 -O2 -std=c++20 x86-64 (AMD64) System V ABI

Intra-register sorting • Fast linear median-of-seven filter • Fast small-kernel convolution • Faster (?) UTF-8 to UTF-32 conversion (with AVX2) • No heavy code, but lots of pictures • Thinking "vertically" CppCon const* psrc) { return _mm512_loadu_ps(psrc); } m0 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 m13 m14 m15 m0 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 m13 m14 m15 psrcCopyright © 2020 Bob Steagall K E W B C m6 m7 m8 m9 m10 m11 m12 m13 m14 m15 f f m2 m3 f f m6 m7 f f f f m12 m13 m14 m15 f 0 0 1 1 0 0 1 1 0 0 0 0 1 1 1 1 fill mask psrcCopyright © 2020 Bob Steagall K E W B C O M P U T I N G 8 CppCon

Ben the count one digit at a time. 3. When done, yell "End of Line" Exercise 7async/concurrency 8async/concurrency GPIO Timer 1 Timer 2 I2C DMA Half-Duplex Serial core 9Sender World View 10Sender async::continue_on(s2) | async::then([] (int i) { return std::to_string(i); }) ; 1 2 3 4 5 6 7 8 auto r = comp | async::sync_wait(); 9 auto [str] = r.value_or(std::make_tuple(""_s)); 10 23Composition async::continue_on(s2) | async::then([] (int i) { return std::to_string(i); }) ; 1 2 3 4 5 6 7 8 auto r = comp | async::sync_wait(); 9 auto [str] = r.value_or(std::make_tuple(""_s)); 10 auto r =

1 MB = 33,725 devices >= 1 MB = 4,964 devicesMicrocontroller Constraints: Limited Storage & Memory 8 < 100kB = 31,098 devices >= 100kB = 7095With so little memory how do you prevent running out of std::vector std::unordered_map std::shared_ptr 111213 Lets not forget about ● std::inplace_vector: p0843r8 voted into C++26 @ St Louis 2024 ISO C++ meetingTIME SPACE So why do firmware developers avoid C++ the problem: Return mismatch 27 /// @returns false if this failed! bool io_expander_level(std::uint8_t p_pin_number, bool p_high_voltage) { // Implementation details... } void some_output_pin::level(bool

platform 7 Processor Memory IO InterconnectComputer platform Processor + Interconnect + Memory 8Computer platform Processor + Interconnect + Memory 9Computer platform Processor + Interconnect MDP and vendor marketing names for multilayer componentsMemory • What about HBM? Not 1024 bits, 8 x 128 instead. Bandwidth will only be high when there is sufficient stream of commands inflight • $2, 38141952 ori $2, $2, 0x8acf dsll $2, $2, 17 daddiu $2, $2, 9903 dsll $2, $2, 18 ori $2, $2, 0xdef0 46 02 02 3c cf 8a 42 34 78 14 02 00 af 26 42 64 b8 14 02 00 f0 de 42 34Code density

'\n'; } std::vector coll1{0, 8, 15, 47, 11, 42, 1}; std::set coll2{0, 8, 15, 47, 11, 42, 1}; print(coll1); print(coll2); Output: 0 8 15 47 11 42 1 0 1 8 11 15 42 47 C++20 template coll1{0, 8, 15, 47, 11, 42, 1}; std::set coll2{0, 8, 15, 47, 11, 42, 1}; Output: 0 8 15 47 11 42 1 0 1 8 11 15 42 47 C++20 ©2024 by josuttis.com 6 C++ std::cout << elem << ' '; } std::cout << '\n'; } std::vector coll1{0, 8, 15, 47, 11, 42, 1}; std::set coll2{0, 8, 15, 47, 11, 42, 1}; print(coll1); print(coll2); print(std::views::take(coll1