From b8e4a5f8d1ccb39e21554754c14bb0ac7742111f Mon Sep 17 00:00:00 2001
From: Jakob Bornecrantz <jakob@collabora.com>
Date: Mon, 1 Apr 2019 17:10:41 +0100
Subject: [PATCH] aux/math: Add simple string hashing function

---
 src/xrt/auxiliary/CMakeLists.txt  |  3 ++-
 src/xrt/auxiliary/math/m_api.h    | 19 +++++++++++++++++++
 src/xrt/auxiliary/math/m_hash.cpp | 20 ++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 src/xrt/auxiliary/math/m_hash.cpp

diff --git a/src/xrt/auxiliary/CMakeLists.txt b/src/xrt/auxiliary/CMakeLists.txt
index 36acf157c..8e7ce6be8 100644
--- a/src/xrt/auxiliary/CMakeLists.txt
+++ b/src/xrt/auxiliary/CMakeLists.txt
@@ -4,8 +4,9 @@
 set(MATH_SOURCE_FILES
 	math/m_api.h
 	math/m_base.cpp
-	math/m_optics.c
 	math/m_eigen_interop.h
+	math/m_hash.cpp
+	math/m_optics.c
 	math/m_quatexpmap.cpp
 	)
 
diff --git a/src/xrt/auxiliary/math/m_api.h b/src/xrt/auxiliary/math/m_api.h
index 16543e1b9..c14df3197 100644
--- a/src/xrt/auxiliary/math/m_api.h
+++ b/src/xrt/auxiliary/math/m_api.h
@@ -36,6 +36,25 @@ extern "C" {
  */
 
 
+/*
+ *
+ * Hash functions.
+ *
+ */
+
+/*!
+ * Generate a hash value from the given string, trailing zero not included.
+ *
+ * Hashing function used is not specified so no garantee of staying the same
+ * between different versions of the software, or even when the same version
+ * is compiled on different platforms/libc++ as it might use std::hash.
+ *
+ * @ingroup aux_math
+ */
+size_t
+math_hash_string(const char *str_c, size_t length);
+
+
 /*
  *
  * Vector functions
diff --git a/src/xrt/auxiliary/math/m_hash.cpp b/src/xrt/auxiliary/math/m_hash.cpp
new file mode 100644
index 000000000..20b8d84e4
--- /dev/null
+++ b/src/xrt/auxiliary/math/m_hash.cpp
@@ -0,0 +1,20 @@
+// Copyright 2019, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Hashing fuction.
+ * @author Jakob Bornecrantz <jakob@collabora.com>
+ * @ingroup aux_math
+ */
+
+#include <string>
+#include "m_api.h"
+
+
+extern "C" size_t
+math_hash_string(const char *str_c, size_t length)
+{
+	std::string str = std::string(str_c, length);
+	std::hash<std::string> str_hash;
+	return str_hash(str);
+}