py: Implement mp_format_float for doubles and use where appropriate

This allows using (almost) the same code for printing floats everywhere,
removes the dependency on sprintf and uses just snprintf and
applies an msvc-specific fix for snprintf in a single place so
nan/inf are now printed correctly.

py/formatfloat.c

@@ -24,10 +24,15 @@
  * THE SOFTWARE.
  */
 
+#include <stdlib.h>
+#include <stdint.h>
+#include "py/formatfloat.h"
+
+#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
 /***********************************************************************
 
-  formatfloat.c  - Ruutine for converting a single-precision floating
-                    point number into a string.
+  Routine for converting a single-precision floating
+  point number into a string.
 
   The code in this funcion was inspired from Fred Bayer's pdouble.c.
   Since pdouble.c was released as Public Domain, I'm releasing this
@@ -39,15 +44,6 @@
 
 ***********************************************************************/
 
-#include <stdlib.h>
-#include <stdint.h>
-
-#include "py/mpconfig.h"
-
-#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
-
-#include "py/formatfloat.h"
-
 // 1 sign bit, 8 exponent bits, and 23 mantissa bits.
 // exponent values 0 and 255 are reserved, exponent can be 1 to 254.
 // exponent is stored with a bias of 127.
@@ -341,4 +337,76 @@ int mp_format_float(float f, char *buf, size_t buf_size, char fmt, int prec, cha
     return s - buf;
 }
 
+#elif MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_DOUBLE
+
+#include <errno.h>
+#include <stdio.h>
+
+#ifdef _MSC_VER
+// For msvc we need to address some quirks in the snprintf implementation:
+// - there is no standard snprintf, it is named _snprintf instead
+// - 'F' format isn't handled so use 'f'
+// - nan and inf are printed as 1.#QNAN and 1.#INF
+#include <math.h>
+#include <string.h>
+
+STATIC int copy_with_sign(char *dest, size_t bufSize, const char *value, char sign) {
+    if (bufSize == 0) {
+        return 0;
+    }
+    size_t numSignChars = 0;
+    if (sign) {
+        *dest = sign;
+        ++numSignChars;
+    }
+    // check total length including terminator
+    size_t length = strlen(value) + 1 + numSignChars;
+    if (length > bufSize) {
+        length = bufSize;
+    }
+    // length without terminator
+    --length;
+    if (length > numSignChars) {
+        memcpy(dest + numSignChars, value, length - numSignChars);
+    }
+    dest[length] = 0;
+    return length;
+}
+
+#define snprintf _snprintf
+#endif
+
+int mp_format_float(double value, char *buf, size_t bufSize, char fmt, int prec, char sign) {
+    if (!buf) {
+        errno = EINVAL;
+        return -1;
+    }
+#ifdef _MSC_VER
+    if (isnan(value)) {
+        return copy_with_sign(buf, bufSize, "nan", sign);
+    } else if (isinf(value)) {
+        return copy_with_sign(buf, bufSize, "inf", value > 0.0 ? sign : '-');
+    } else {
+        if (fmt == 'F') {
+            fmt = 'f';
+        }
+#endif
+        char fmt_buf[6];
+        char *fmt_s = fmt_buf;
+
+        *fmt_s++ = '%';
+        if (sign) {
+            *fmt_s++ = sign;
+        }
+        *fmt_s++ = '.';
+        *fmt_s++ = '*';
+        *fmt_s++ = fmt;
+        *fmt_s = '\0';
+
+        return snprintf(buf, bufSize, fmt_buf, prec, value);
+#ifdef _MSC_VER
+    }
+#endif
+}
+
 #endif