Where does the formula of BAUD comes from in SERCOM::initMasterWIRE( uint32_t baudrate )

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I've read in SAMD21 datasheet that the frequency generated for the I2C SCL line depends on the BAUD register.

Accoring to the documentation, this field should be generated using the following ecuations:

Bits 7:0 – BAUD[7:0] Master Baud Rate This bit field is used to derive the SCL high time if BAUD.BAUDLOW is non-zero. If BAUD.BAUDLOW is zero, BAUD will be used to generate both high and low periods of the SCL. For more information on how to calculate the frequency, see SERCOM 25.6.2.3 Clock Generation – Baud-Rate Generator.

I've seen in the code inside this method that clock frequency is generated using the following line:

// Synchronous arithmetic baudrate
  sercom->I2CM.BAUD.bit.BAUD = SystemCoreClock / ( 2 * baudrate) - 5 - (((SystemCoreClock / 1000000) * WIRE_RISE_TIME_NANOSECONDS) / (2 * 1000));

I was willing to know where this ecuation comes from as in the documentation says that for Synchronous baudrate the following ecuation should be used:

From that point of view, should that line be something like this?:

// Synchronous arithmetic baudrate
  sercom->I2CM.BAUD.bit.BAUD = SystemCoreClock / ( 2 * baudrate) - 1;

The datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/SAM_D21_DA1_Family_DataSheet_DS40001882F.pdf, page 412-413