lib/libm: Remove implementation of log2f, use MP_NEED_LOG2 instead.

lib/libm/math.c

@@ -48,16 +48,6 @@ float copysignf(float x, float y) {
 }
 #endif
 
-// some compilers define log2f in terms of logf
-#ifdef log2f
-#undef log2f
-#endif
-// some compilers have _M_LN2 defined in math.h, some don't
-#ifndef _M_LN2
-#define _M_LN2 (0.69314718055994530942)
-#endif
-float log2f(float x) { return logf(x) / (float)_M_LN2; }
-
 static const float _M_LN10 = 2.30258509299404; // 0x40135d8e
 float log10f(float x) { return logf(x) / (float)_M_LN10; }
 

ports/stm32/mpconfigport.h

@@ -335,6 +335,9 @@ static inline mp_uint_t disable_irq(void) {
     } while (0);
 #endif
 
+// We need an implementation of the log2 function which is not a macro
+#define MP_NEED_LOG2 (1)
+
 // There is no classical C heap in bare-metal ports, only Python
 // garbage-collected heap. For completeness, emulate C heap via
 // GC heap. Note that MicroPython core never uses malloc() and friends,