printf_unsigned_integer_with_commas/snprintf_uint_commas.c at main · Serialcomms/printf_unsigned_integer_with_commas · GitHub

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void snprintf_uint_commas(uint unsigned_integer, char printf_result[14U]) {

  // Maximum unsigned integer value = 2,147,483,647
  // Maximum digit_10 value = 2 (2,nnn,nnn,nnn)

  // IMPORTANT: minimum printf_result size = 14 characters
  // = 10 digits, 3 commas and 1 null terminator character
  // -Wstringop-overflow may be generated if buffer too small

  const size_t buffer_size = 14U;

  uint8_t *printf_buffer = printf_result;

  uint digit_10_only = (unsigned_integer / (uint)1e9);
  uint digits_9_to_7 = (unsigned_integer / (uint)1e6) % 1000U;
  uint digits_6_to_4 = (unsigned_integer / (uint)1e3) % 1000U;
  uint digits_3_to_1 = (unsigned_integer / (uint)1e0) % 1000U;

  if (unsigned_integer < (uint)1e3) {           // < 1,000

    snprintf(printf_buffer, buffer_size, "%u",
      digits_3_to_1);

  } else if (unsigned_integer < (uint)1e6) {    // < 1,000,000

    snprintf(printf_buffer, buffer_size, "%u,%03u",
      digits_6_to_4, digits_3_to_1);

  } else if  (unsigned_integer < (uint)1e9) {   // < 1,000,000,000

    snprintf(printf_buffer, buffer_size, "%u,%03u,%03u",
      digits_9_to_7, digits_6_to_4, digits_3_to_1);

  } else {                                      // > 999,999,999

    snprintf(printf_buffer, buffer_size, "%u,%03u,%03u,%03u",
      digit_10_only, digits_9_to_7, digits_6_to_4, digits_3_to_1);

  }

}