Add CRC8 calculation subsystem to quantum (#12641)

* Intended usage is data validation in split transport code.
* Default space efficient algorithm.
* Opt-in fast table based algorithmn with #define CRC8_USE_TABLE switch.
* Define switches for size and speed optimized versions, the default is size
  optimized by using uint_least8_t as datatype for calculations.
  * #define CRC8_OPTIMIZE_SPEED uses uint_fast8_t as datatype for
    calculations, this only affects 32-bit Archs like ARM and RISC-V.
* Placeholder crc_init() function for hardware backed crc calculation,
  not implemented yet.

1 files changed, 44 insertions, 0 deletions

diff --git a/quantum/crc.h b/quantum/crc.h
new file mode 100644
index 000000000..c17f5888e
--- /dev/null
+++ b/quantum/crc.h
@@ -0,0 +1,44 @@
+/* Copyright 2021 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "quantum.h"
+
+/**
+ * The type of the CRC values.
+ *
+ * This type must be big enough to contain at least 8 bits.
+ */
+#if defined(CRC8_OPTIMIZE_SPEED)
+typedef uint_fast8_t crc_t;
+#else
+typedef uint_least8_t crc_t;
+#endif
+
+/**
+ * Initialize crc subsystem.
+ */
+__attribute__((weak)) void crc_init(void);
+
+/**
+ * Generate CRC8 value from given data.
+ *
+ * \param[in] data     Pointer to a buffer of \a data_len bytes.
+ * \param[in] data_len Number of bytes in the \a data buffer.
+ * \return             The calculated crc value.
+ */
+__attribute__((weak)) uint8_t crc8(const void *data, size_t data_len);
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