replace faulty n_ftoa.c implementation that truncated doubles upon co…

[rayozzie]

For historical reasons (trying to get it to work in extremely low memory on a 16-bit MCU) I had an awful implementation of the JNtoA() function. This replaces it with a better implementation, tested against a golang equivalent and tested with the Arduino program below.

(In case you're wondering, we can't just use snprintf to do the conversions because most microcontroller libraries, including newlib, omit floating point support by default for memory reasons.)

test.ino

#include <Notecard.h>
#include <Wire.h>

#ifdef NOTE_FLOAT
#error "we're not even using double on this platform"
#endif

#define serialNotecard Serial1
#define serialDebugOut Serial
Notecard notecard;

void test(JNUMBER f)
{
	float g;
	char buf1[64], buf2[64];
	JNtoA(f, buf1, -1);
	g = JAtoN(buf1, NULL);
	JNtoA(g, buf2, -1);
	if (strcmp(buf1, buf2) != 0) {
		printf("%s %s", buf1, buf2);
	}
    J *req = JCreateObject();
	if (req == NULL) {
		printf(" REQ-ERROR\n");
	} else {
		JAddNumberToObject(req, "test", f);
		char *reqJSON = JPrintUnformatted(req);
		JDelete(req);
		if (reqJSON == NULL) {
			printf(" PRINT-ERROR\n");
		} else {
			printf(" %s", reqJSON);
			JFree(reqJSON);
		}
	}
	printf("\n");

}

void setup()
{
    delay(2500);
    serialDebugOut.begin(115200);
    notecard.setDebugOutputStream(serialDebugOut);
    notecard.begin(serialNotecard, 9600);

	int limit = 28;
	double f = 1.0;

	printf("sizeof(double) == %d\n", sizeof(f));

	// Test numbers that can be represented in floats, high-to-small
	for (int i = 0; i < limit; i++) {
		test(f);
		f = f / 2;
	}
	// Test numbers that can be represented in floats, small-to-high
	for (int i = 0; i < limit; i++) {
		f = f * 2;
		test(f);
	}
	// Test numbers that can be represented in floats, higher than zero
	for (int i = 0; i < limit*2; i++) {
		f = f * 2;
		test(f);
	}

}

void loop()
{
}