Add JSON API

src/str.c

@@ -397,3 +397,49 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
   if (n < len) buf[n] = '\0';
   return n;
 }
+
+double mg_atod(const char *p, int len, int *numlen) {
+  double d = 0.0;
+  int i = 0, sign = 1;
+
+  // Sign
+  if (i < len && *p == '-') {
+    sign = -1, i++;
+  } else if (i < len && *p == '+') {
+    i++;
+  }
+
+  // Decimal
+  for (; i < len && is_digit(p[i]); i++) {
+    d *= 10.0;
+    d += p[i] - '0';
+  }
+  d *= sign;
+
+  // Fractional
+  if (i < len && p[i] == '.') {
+    double frac = 0.0, base = 0.1;
+    i++;
+    for (; i < len && is_digit(p[i]); i++) {
+      frac += base * (p[i] - '0');
+      base /= 10.0;
+    }
+    d += frac * sign;
+  }
+
+  // Exponential
+  if (i < len && (p[i] == 'e' || p[i] == 'E')) {
+    int j, exp = 0, minus = 0;
+    i++;
+    if (i < len && p[i] == '-') minus = 1, i++;
+    if (i < len && p[i] == '+') i++;
+    while (i < len && is_digit(p[i]) && exp < 308)
+      exp = exp * 10 + (p[i++] - '0');
+    if (minus) exp = -exp;
+    for (j = 0; j < exp; j++) d *= 10.0;
+    for (j = 0; j < -exp; j++) d /= 10.0;
+  }
+
+  if (numlen != NULL) *numlen = i;
+  return d;
+}