strtof: Add strtof() as simply a compy of strtod with types and limits changed

include/stdlib.h

@@ -80,18 +80,11 @@
 #  define environ get_environ_ptr()
 #endif
 
-/* The functions strtof() and strtold() are not currently implemented in
- * NuttX.  Ideally, custom implementations of these functions would be
- * provided because:
- *
- *   strtof() - Some MCUs, such as the Cortex-M4F, have built in 32-bit FPU.
- *     A true implementation could exploit the improved performance by the
- *     the FPU.
- *   strtold() - Of course, there is a loss of 32-bits of accuracy in this
- *     conversion.
+/* The function strtold() is not currently implemented in NuttX.  Ideally, a
+ * custom implementation should be provided because, of course, there is a
+ * loss of 32-bits of accuracy in this conversion.
  */
 
-#define strtof(a,b)  (float)strtod(a,b)
 #define strtold(a,b) (long double)strtod(a,b)
 
 /****************************************************************************
@@ -205,6 +198,7 @@ unsigned long long strtoull(FAR const char *nptr, FAR char **endptr,
                             int base);
 #endif
 double_t  strtod(FAR const char *str, FAR char **endptr);
+float     strtof(FAR const char *str, FAR char **endptr);
 
 #define atoi(nptr)  ((int)strtol((nptr), NULL, 10))
 #define atol(nptr)  strtol((nptr), NULL, 10)

libc/stdlib/Make.defs

@@ -39,7 +39,7 @@ CSRCS += lib_abs.c lib_abort.c lib_div.c lib_ldiv.c lib_lldiv.c
 CSRCS += lib_imaxabs.c lib_itoa.c lib_labs.c lib_llabs.c
 CSRCS += lib_bsearch.c lib_rand.c lib_qsort.c lib_srand.c
 CSRCS += lib_strtol.c lib_strtoll.c lib_strtoul.c lib_strtoull.c
-CSRCS += lib_strtod.c lib_checkbase.c
+CSRCS += lib_strtod.c lib_strtof.c lib_checkbase.c
 
 ifeq ($(CONFIG_FS_WRITABLE),y)
 CSRCS += lib_mktemp.c lib_mkstemp.c

libc/stdlib/lib_strtod.c

@@ -92,7 +92,7 @@ double_t strtod(FAR const char *str, FAR char **endptr)
   double_t number;
   int exponent;
   int negative;
-  char *p = (char *) str;
+  FAR char *p = (FAR char *) str;
   double p10;
   int n;
   int num_digits;