BLI_math: add simple helper to get amount of 'integer' digits in a float number.

source/blender/blenlib/BLI_math_base.h

@@ -138,6 +138,9 @@ MINLINE int signum_i(float a);
 
 MINLINE float power_of_2(float f);
 
+MINLINE int integer_digits_f(const float f);
+MINLINE int integer_digits_d(const double d);
+
 /* these don't really fit anywhere but were being copied about a lot */
 MINLINE int is_power_of_2_i(int n);
 MINLINE int power_of_2_max_i(int n);

source/blender/blenlib/intern/math_base_inline.c

@@ -314,6 +314,21 @@ MINLINE int signum_i(float a)
 	else          return  0;
 }
 
+/** Returns number of (base ten) *significant* digits of integer part of given float
+ * (negative in case of decimal-only floats, 0.01 returns -1 e.g.). */
+MINLINE int integer_digits_f(const float f)
+{
+	return (f == 0.0f) ? 0 : (int)floor(log10(fabs(f))) + 1;
+}
+
+/** Returns number of (base ten) *significant* digits of integer part of given double
+ * (negative in case of decimal-only floats, 0.01 returns -1 e.g.). */
+MINLINE int integer_digits_d(const double d)
+{
+	return (d == 0.0) ? 0 : (int)floor(log10(fabs(d))) + 1;
+}
+
+
 /* Internal helpers for SSE2 implementation.
  *
  * NOTE: Are to be called ONLY from inside `#ifdef __SSE2__` !!!