Other Alias

ggidev-add_3, ggidev-sub_3, ggidev-divmod_3## SYNOPSIS

#include <ggi/internal/triple-int.h>

unsigned *add_3(unsigned l[3], unsigned r[3]);

unsigned *sub_3(unsigned l[3], unsigned r[3]);

unsigned *mul_3(unsigned l[3], unsigned r[3]);

unsigned *divmod_3(unsigned a[3], unsigned b[3],

unsigned q[3], unsigned r[3]);

## DESCRIPTION

**add_3**adds

**r**to

**l**. Equivalent to l+=r.

**sub_3** subtracts **r** from **l**. Equivalent to l-=r.

**mul_3** multiplies **r** with **l**. Equivalent to l*=r.

**divmod_3** calculates the quotient **q** and the remainder **r** of **a**/**b**
such that **a** = **q** * **b** + **r**. Equivalent to r=a%b,q=a/b.

Multiplication and division needs to operate on **limbs** to perform long
multiplication and division. If a type with twice the precision of an
**unsigned** is found (typically the **long long** type), **unsigned** is used
as the **limb**. If not, half the bits of an **unsigned** are used as the
**limb**.

The division algorithm is probably similar to the algorithm described by Donald E. Knuth in "The Art of Computer Programming", volume 2, but the author of the code has not actually read that book, only a short description of the algorithm. The degree of similarity is therefore uncertain.

## RETURN VALUE

**add_3**,

**sub_3**and

**mul_3**all return a pointer to

**l**which has been updated in place.

divmod_3 returns a pointer to the quotient **q**.

## EXAMPLES

Some binary arithmetic operations on**triple-ints**:

unsigned x[3], y[3], q[3], r[3]; assign_int_3(x, 4); assign_int_3(y, 5); add_3(x, y); /* x == 9 */ assign_int_3(q, 3); sub_3(x, q); /* x == 6 */ mul_3(x, q); /* x == 18 */ divmod_3(x, y, q, r); /* q == 3, r == 3 */