From 829835b1ede07981027da493df0179638b29947d Mon Sep 17 00:00:00 2001
From: Daniel Bevenius <daniel.bevenius@gmail.com>
Date: Sun, 19 May 2024 07:18:40 +0200
Subject: [PATCH] blas: add initial OpenBLAS exploration code

Signed-off-by: Daniel Bevenius <daniel.bevenius@gmail.com>
---
 fundamentals/blas/openblas/.gitignore       |  1 +
 fundamentals/blas/openblas/Makefile         | 20 ++++++++++
 fundamentals/blas/openblas/README.md        | 15 +++++++
 fundamentals/blas/openblas/src/gemm.c       | 43 +++++++++++++++++++++
 fundamentals/blas/openblas/src/vector_add.c | 20 ++++++++++
 5 files changed, 99 insertions(+)
 create mode 100644 fundamentals/blas/openblas/.gitignore
 create mode 100644 fundamentals/blas/openblas/Makefile
 create mode 100644 fundamentals/blas/openblas/README.md
 create mode 100644 fundamentals/blas/openblas/src/gemm.c
 create mode 100644 fundamentals/blas/openblas/src/vector_add.c

diff --git a/fundamentals/blas/openblas/.gitignore b/fundamentals/blas/openblas/.gitignore
new file mode 100644
index 00000000..ba077a40
--- /dev/null
+++ b/fundamentals/blas/openblas/.gitignore
@@ -0,0 +1 @@
+bin
diff --git a/fundamentals/blas/openblas/Makefile b/fundamentals/blas/openblas/Makefile
new file mode 100644
index 00000000..4645231e
--- /dev/null
+++ b/fundamentals/blas/openblas/Makefile
@@ -0,0 +1,20 @@
+CC = gcc
+SRCDIR = src
+BINDIR = bin
+
+SOURCES := $(wildcard $(SRCDIR)/*.c)
+TARGETS := $(patsubst $(SRCDIR)/%.c, %, $(SOURCES))
+
+all: $(TARGETS)
+
+$(TARGETS): % : $(SRCDIR)/%.c | bindir
+	$(CC) -o ${BINDIR}/$@ $< -lopenblas
+
+bindir: bin
+
+bin: 
+	@mkdir -p $(BINDIR)
+
+.PHONY: clean
+clean:
+	@${RM} -rf $(BINDIR)
diff --git a/fundamentals/blas/openblas/README.md b/fundamentals/blas/openblas/README.md
new file mode 100644
index 00000000..f947f22e
--- /dev/null
+++ b/fundamentals/blas/openblas/README.md
@@ -0,0 +1,15 @@
+## OpenBLAS
+This is an implementation of BLAS for CPUs.
+
+
+### Installation
+```console
+$ sudo apt update
+$ sudo apt install libopenblas-dev
+```
+
+### Building
+```console
+$ make vector_add
+```
+
diff --git a/fundamentals/blas/openblas/src/gemm.c b/fundamentals/blas/openblas/src/gemm.c
new file mode 100644
index 00000000..e232a765
--- /dev/null
+++ b/fundamentals/blas/openblas/src/gemm.c
@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <cblas.h>
+
+int main() {
+    const int M = 2; // Number of rows of matrix A and C
+    const int N = 2; // Number of columns of matrix B and C
+    const int K = 3; // Number of columns of matrix A and rows of matrix B
+
+    float alpha = 1.0f;
+    float beta = 0.0f;
+
+    // Declare matrices A, B, and C
+    float A[M*K];
+    float B[K*N];
+    float C[M*N];
+
+    // Initialize matrices A and B with given values
+    A[0] = 1; A[1] = 2; A[2] = 3;
+    A[3] = 4; A[4] = 5; A[5] = 6;
+
+    B[0] = 1; B[1] = 2;
+    B[2] = 3; B[3] = 4;
+    B[4] = 5; B[5] = 6;
+
+    // Initialize matrix C with initial non-zero values
+    C[0] = 0; C[1] = 0;
+    C[2] = 0; C[3] = 0;
+
+    // Perform matrix multiplication C = alpha * A * B + beta * C
+    cblas_sgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, M, N, K, alpha, A, K, B, N, beta, C, N);
+
+    // Print the resulting matrix C
+    printf("Resulting matrix C:\n");
+    for (int i = 0; i < M; ++i) {
+        for (int j = 0; j < N; ++j) {
+            printf("%f ", C[i*N + j]);
+        }
+        printf("\n");
+    }
+
+    return 0;
+}
+
diff --git a/fundamentals/blas/openblas/src/vector_add.c b/fundamentals/blas/openblas/src/vector_add.c
new file mode 100644
index 00000000..21bf71fc
--- /dev/null
+++ b/fundamentals/blas/openblas/src/vector_add.c
@@ -0,0 +1,20 @@
+#include <cblas.h>
+#include <stdio.h>
+
+int main() {
+    int n = 5;
+    float x[] = {1, 2, 3, 4, 5};
+    float y[] = {5, 4, 3, 2, 1};
+    float alpha = 1.0;
+
+    // y = alpha * x + y
+    cblas_saxpy(n, alpha, x, 1, y, 1);
+
+    for (int i = 0; i < n; i++) {
+        printf("%f ", y[i]);
+    }
+    printf("\n");
+
+    return 0;
+}
+