String(unsigned long) constructor reverses digits, e.g. 10 becomes "01"

[marcboon]

Arduino 1.8.15
ESP32 v2.0.0-rc-1
ESP32-S2-WROVER (Saola 1)

String() constructor from unsigned long reverses digits.
Code:

void setup() {
  Serial.begin(115200);
  delay(100);
    
  for(unsigned long ul = 0; ul < 25; ul++) {
    Serial.println(String(ul)); 
  }
}

void loop() {
}

Output:

0
1
2
3
4
5
6
7
8
9
01
11
21
31
41
51
61
71
81
91
02
12
22
32
42

After some more testing I found that the problem is actually with ultoa(), and also ltoa(). The String(unsigned long) constructor uses ultoa() for the conversion, while String(long) uses sprintf("%ld") when base is 10 (which works as expected), and ltoa() for other cases, which fail.
So, both ltoa() and ultoa() reverse digits.

  unsigned long value = 123456789;
  char buf[10];
  ultoa(value, buf, 10);
  Serial.print(buf);

produces "987654321"

[me-no-dev]

try RC2

[marcboon]

try RC2

I didn't realize it was released already. Thanks, will do!

[marcboon]

Fixed in RC2