Buf serializing code

buf/main.c

@@ -0,0 +1,87 @@
+#include "buf.h"
+#include <assert.h>
+#include <math.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+/*
+ * Inspired by Vedders bldc code.
+ *
+ * I stumbled upon this beautiful solution when reading the motor control firmware from the vesc project.
+ * It effectively packs/serializes data into a buffer that could easily be sent over, say, uart. The original solution
+ * also does fp magic in a seemingly portable way.
+ *
+ * For the original GPLv3 licensed source, see:
+ *      https://github.com/vedderb/bldc/blob/master/util/buffer.c
+ *
+ * For a more permissive MIT licensed source, see:
+ *      https://github.com/waas-rent/vesc_can_sdk/blob/main/vesc_buffer.c
+ */
+
+/* This buffer can live anywhere, make sure its long enough to hold your data! */
+uint8_t buf[100];
+
+/* Float comparison with error tolerance */
+static inline bool float_eq(float a, float b, float epsilon) {
+    return fabsf(a - b) < epsilon;
+}
+
+int main(void) {
+    /* This index acts as a read/write pointer */
+    size_t index = 0;
+
+    /* Declare and define data to be serialized */
+    uint8_t uint8bit = 8;
+    int16_t int16bit = 16;
+    int32_t int32bit = 32;
+    float   float32bit = 1337.42;
+
+    /* When appending the buffer, the index is passed along and incremented accordingly */
+    buf_append_u8(buf, uint8bit, &index);
+    assert(index == 1);
+    buf_append_i16(buf, int16bit, &index);
+    assert(index == 3);
+    buf_append_i32(buf, int32bit, &index);
+    assert(index == 7);
+    buf_append_f32(buf, float32bit, &index);
+    assert(index == 11);
+
+    /*
+     * Note that after we're done appending, the index value will hold the
+     * length of the 'message', so, if you're piping this through uart or some
+     * other medium, you dont have to send the entire buffer length, just send
+     * up to the index.
+     *
+     * For bonus points for doing it vesc-style, prepend the message with the message type (a
+     * byte-length enum shared by both sides, for example), as well as a message
+     * length. You could also use the last two bytes of every message for a
+     * crc16 checksum for error resilience.
+     */
+
+    /* Zero the original data */
+    uint8bit = 0;
+    int16bit = 0;
+    int32bit = 0;
+    float32bit = 0.f;
+
+    /* Read from beginning */
+    index = 0;
+
+    /* Re-populate our original data */
+    uint8bit = buf_read_u8(buf, &index);
+    assert(index == 1);
+    int16bit = buf_read_i16(buf, &index);
+    assert(index == 3);
+    int32bit = buf_read_i32(buf, &index);
+    assert(index == 7);
+    float32bit = buf_read_f32(buf, &index);
+    assert(index == 11);
+
+    /* Assert that it all worked out */
+    assert(uint8bit == 8);
+    assert(int16bit == 16);
+    assert(int32bit == 32);
+    assert(float_eq(float32bit, 1337.42, 0.01));
+
+    printf("All asserts passed!\n");
+}