Re: [avr-gcc-list] Rounded integral division in preprocessor

[Bob Paddock]

On Fri, Feb 5, 2010 at 1:44 AM, Johannes Bauer <address@hidden> wrote:
> Dear list,
>
> I'm trying to do rounded (opposed to truncated) integer division with
> avr-gcc with using only preprocessor magic. This proves to be difficult: The
> current code I'm using is
>
> #define __IDIV(x, y)    (long)(((long)x + ((long)y / 2L)) / (long)y)
> #define IDIV(x, y)      (__IDIV((x), (y)))

> Is there another way to do it?

/*
 * #define UART_BAUD_SELECT (F_CPU/(UART_BAUD_RATE*16L)-1)
 *
 * When doing integer divide it is usually better to round to the nearest
 * integer, rather than to the lowest (which the above expression does).
 *
 * Add 0.5 (i.e. half the value of the denominator)
 * to the numerator before the division.  This can be achieved in the
 * following way:
 *
 * #define UART_BAUD_SELECT ((F_CPU + UART_BAUD_RATE * 8L) /\
 *                             (UART_BAUD_RATE * 16L) - 1)
 * - Neil Johnson AVR-GCC List
 */

#define UART_BAUD_CALCULATE(UART_BAUD_RATE) ((F_CPU + UART_BAUD_RATE *
8L) / (UART_BAUD_RATE * 16L) - 1)



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