simd: add initial simd exploration code (wip)

Signed-off-by: Daniel Bevenius <[email protected]>

fundamentals/simd/.gitignore

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+bin

fundamentals/simd/Makefile

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+CXX = g++
+CXXFLAGS = -g -Wall -mavx2 -Wno-unused-variable
+
+SRCDIR = src
+BINDIR = bin
+
+SOURCES := $(wildcard $(SRCDIR)/*.cpp)
+TARGETS := $(patsubst $(SRCDIR)/%.cpp, %, $(SOURCES))
+
+all: $(TARGETS)
+
+$(TARGETS): % : $(SRCDIR)/%.cpp | bindir
+	$(CXX) $(CXXFLAGS) -o ${BINDIR}/$@ $<
+
+bindir: bin
+bin: 
+	@mkdir -p $(BINDIR)

fundamentals/simd/README.md

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+## Single Instruction, Multiple Data (SIMD)
+
+### Introduction
+TODO:
+
+### Machine specific options/support
+If you just try to compile a program using SIMD instructions, you may get the
+following error message:
+```console
+$ make add
+gcc -g -Wall  -Wno-unused-variable   -o bin/add src/add.cpp
+src/add.cpp: In function ‘int main()’:
+src/add.cpp:11:52: warning: AVX vector return without AVX enabled changes the ABI [-Wpsabi]
+   11 |     __m256i a = _mm256_loadu_si256((__m256i*)array1);
+      |                                                    ^
+In file included from /usr/lib/gcc/x86_64-linux-gnu/11/include/immintrin.h:43,
+                 from src/add.cpp:1:
+/usr/lib/gcc/x86_64-linux-gnu/11/include/avxintrin.h:933:1: error: inlining failed in call to ‘always_inline’ ‘void _mm256_storeu_si256(__m256i_u*, __m256i)’: target specific option mismatch
+  933 | _mm256_storeu_si256 (__m256i_u *__P, __m256i __A)
+      | ^~~~~~~~~~~~~~~~~~~
+src/add.cpp:18:24: note: called from here
+   18 |     _mm256_storeu_si256((__m256i*)result, c);
+      |     ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
+In file included from /usr/lib/gcc/x86_64-linux-gnu/11/include/immintrin.h:47,
+                 from src/add.cpp:1:
+/usr/lib/gcc/x86_64-linux-gnu/11/include/avx2intrin.h:119:1: error: inlining failed in call to ‘always_inline’ ‘__m256i _mm256_add_epi32(__m256i, __m256i)’: target specific option mismatch
+  119 | _mm256_add_epi32 (__m256i __A, __m256i __B)
+      | ^~~~~~~~~~~~~~~~
+src/add.cpp:15:33: note: called from here
+   15 |     __m256i c = _mm256_add_epi32(a, b);  // _epi32 denotes 32-bit integer vectors
+      |                 ~~~~~~~~~~~~~~~~^~~~~~
+In file included from /usr/lib/gcc/x86_64-linux-gnu/11/include/immintrin.h:43,
+                 from src/add.cpp:1:
+/usr/lib/gcc/x86_64-linux-gnu/11/include/avxintrin.h:927:1: error: inlining failed in call to ‘always_inline’ ‘__m256i _mm256_loadu_si256(const __m256i_u*)’: target specific option mismatch
+  927 | _mm256_loadu_si256 (__m256i_u const *__P)
+      | ^~~~~~~~~~~~~~~~~~
+src/add.cpp:12:35: note: called from here
+   12 |     __m256i b = _mm256_loadu_si256((__m256i*)array2);
+      |                 ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
+In file included from /usr/lib/gcc/x86_64-linux-gnu/11/include/immintrin.h:43,
+                 from src/add.cpp:1:
+/usr/lib/gcc/x86_64-linux-gnu/11/include/avxintrin.h:927:1: error: inlining failed in call to ‘always_inline’ ‘__m256i _mm256_loadu_si256(const __m256i_u*)’: target specific option mismatch
+  927 | _mm256_loadu_si256 (__m256i_u const *__P)
+      | ^~~~~~~~~~~~~~~~~~
+src/add.cpp:11:35: note: called from here
+   11 |     __m256i a = _mm256_loadu_si256((__m256i*)array1);
+      |                 ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
+make: *** [Makefile:13: add] Error 1
+```
+In this case we nee to add the 'm'achine specific option `avx2` flag to the
+compilation command:
+```console
+$ g++ -g -Wall -mavx2 -Wno-unused-variable -o bin/add src/add.cpp
+```

fundamentals/simd/src/add.cpp

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+#include <immintrin.h>
+#include <iostream>
+
+int main() {
+    int array1[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+    int array2[8] = {8, 7, 6, 5, 4, 3, 2, 1};
+    int result[8] = {0};
+
+    __m256i a = _mm256_loadu_si256((__m256i*)array1);
+    __m256i b = _mm256_loadu_si256((__m256i*)array2);
+
+    __m256i c = _mm256_add_epi32(a, b);  // _epi32 denotes 32-bit integer vectors
+
+    _mm256_storeu_si256((__m256i*)result, c);
+
+    for (int i = 0; i < 8; i++) {
+        std::cout << "result[" << i << "] = " << result[i] << std::endl;
+    }
+
+    return 0;
+}
+