sys/frac: make gcd32() public

A function to calculate the greatest common divisor is generally useful.
In turn declare the internal `frac_long_divide()` as `static`, it's
not used anywhere outside this module and has no public header.

sys/frac/frac.c

@@ -24,15 +24,7 @@
 #define ENABLE_DEBUG (0)
 #include "debug.h"
 
-/**
- * @brief   compute greatest common divisor of @p u and @p v
- *
- * @param[in]   u    first operand
- * @param[in]   v    second operand
- *
- * @return  Greatest common divisor of @p u and @p v
- */
-static uint32_t gcd32(uint32_t u, uint32_t v)
+uint32_t gcd32(uint32_t u, uint32_t v)
 {
     /* Source: https://en.wikipedia.org/wiki/Binary_GCD_algorithm#Iterative_version_in_C */
     unsigned shift;
@@ -81,7 +73,7 @@ static uint32_t gcd32(uint32_t u, uint32_t v)
     return u << shift;
 }
 
-uint32_t frac_long_divide(uint32_t num, uint32_t den, int *prec, uint32_t *rem)
+static uint32_t frac_long_divide(uint32_t num, uint32_t den, int *prec, uint32_t *rem)
 {
     /* Binary long division with adaptive number of fractional bits */
     /* The result will be a Qx.y number where x is the number of bits in the

sys/include/frac.h

@@ -55,6 +55,16 @@ typedef struct {
     uint8_t shift; /**< exponent */
 } frac_t;
 
+/**
+ * @brief   Compute greatest common divisor of @p u and @p v
+ *
+ * @param[in]   u    first operand
+ * @param[in]   v    second operand
+ *
+ * @return  Greatest common divisor of @p u and @p v
+ */
+uint32_t gcd32(uint32_t u, uint32_t v);
+
 /**
  * @brief   Initialize frac_t struct
  *