BLI_math: add floor_power_of_10, ceil_power_of_10

Add utility functions to get the floor/ceiling of a float value
to the next power of 10.

source/blender/blenlib/BLI_math_base.h

@@ -219,6 +219,9 @@ MINLINE unsigned int round_db_to_uint_clamp(double a);
 int pow_i(int base, int exp);
 double double_round(double x, int ndigits);
 
+float floor_power_of_10(float f);
+float ceil_power_of_10(float f);
+
 #ifdef BLI_MATH_GCC_WARN_PRAGMA
 #  pragma GCC diagnostic pop
 #endif

source/blender/blenlib/intern/math_base.c

@@ -79,3 +79,39 @@ double double_round(double x, int ndigits)
   /* if computation resulted in overflow, raise OverflowError */
   return z;
 }
+
+/**
+ * Floor to the nearest power of 10, e.g.:
+ * - 15.0 -> 10.0
+ * - 0.015 -> 0.01
+ * - 1.0 -> 1.0
+ *
+ * \param f: Value to floor, must be over 0.0.
+ * \note If we wanted to support signed values we could if this becomes necessary.
+ */
+float floor_power_of_10(float f)
+{
+  BLI_assert(!(f < 0.0f));
+  if (f != 0.0f) {
+    return 1.0f / (powf(10.0f, ceilf(log10f(1.0f / f))));
+  }
+  return 0.0f;
+}
+
+/**
+ * Ceiling to the nearest power of 10, e.g.:
+ * - 15.0 -> 100.0
+ * - 0.015 -> 0.1
+ * - 1.0 -> 1.0
+ *
+ * \param f: Value to ceiling, must be over 0.0.
+ * \note If we wanted to support signed values we could if this becomes necessary.
+ */
+float ceil_power_of_10(float f)
+{
+  BLI_assert(!(f < 0.0f));
+  if (f != 0.0f) {
+    return 1.0f / (powf(10.0f, floorf(log10f(1.0f / f))));
+  }
+  return 0.0f;
+}

source/blender/blenlib/tests/BLI_math_base_test.cc

@@ -113,3 +113,21 @@ TEST(math_base, Log2CeilU)
   EXPECT_EQ(log2_ceil_u(9), 4);
   EXPECT_EQ(log2_ceil_u(123456), 17);
 }
+
+TEST(math_base, CeilPowerOf10)
+{
+  EXPECT_EQ(ceil_power_of_10(0), 0);
+  EXPECT_EQ(ceil_power_of_10(1), 1);
+  EXPECT_EQ(ceil_power_of_10(1e-6f), 1e-6f);
+  EXPECT_NEAR(ceil_power_of_10(100.1f), 1000.0f, 1e-4f);
+  EXPECT_NEAR(ceil_power_of_10(99.9f), 100.0f, 1e-4f);
+}
+
+TEST(math_base, FloorPowerOf10)
+{
+  EXPECT_EQ(floor_power_of_10(0), 0);
+  EXPECT_EQ(floor_power_of_10(1), 1);
+  EXPECT_EQ(floor_power_of_10(1e-6f), 1e-6f);
+  EXPECT_NEAR(floor_power_of_10(100.1f), 100.0f, 1e-4f);
+  EXPECT_NEAR(floor_power_of_10(99.9f), 10.0f, 1e-4f);
+}