module bignum

// Wrapper for https://github.com/kokke/tiny-bignum-c

#flag -I @VROOT/thirdparty/bignum
#flag @VROOT/thirdparty/bignum/bn.o
#include "bn.h"

const (
	STRING_BUFFER_SIZE = 8192
)

pub struct Number {
	array [32]u32
}

fn C.bignum_init( n &Number )
fn C.bignum_from_int( n &Number, i u64 )
fn C.bignum_to_int( n &Number ) int
fn C.bignum_from_string( n &Number, s byteptr, nbytes int)
fn C.bignum_to_string( n &Number, s byteptr, maxsize int)

fn C.bignum_add( a &Number, b &Number, c &Number) // c = a + b
fn C.bignum_sub( a &Number, b &Number, c &Number) // c = a - b
fn C.bignum_mul( a &Number, b &Number, c &Number) // c = a * b
fn C.bignum_div( a &Number, b &Number, c &Number) // c = a / b
fn C.bignum_mod( a &Number, b &Number, c &Number) // c = a % b
fn C.bignum_divmod( a &Number, b &Number, c &Number, d &Number)  // c = a/b d=a%b

fn C.bignum_and( a &Number, b &Number, c &Number) // c = a & b
fn C.bignum_or( a &Number, b &Number, c &Number)  // c = a | b
fn C.bignum_xor( a &Number, b &Number, c &Number) // c = a xor b
fn C.bignum_lshift( a &Number, b &Number, nbits int) // b = a << nbits
fn C.bignum_rshift( a &Number, b &Number, nbits int) // b = a >> nbits

fn C.bignum_cmp( a &Number, b &Number) int
fn C.bignum_is_zero( a &Number) int
fn C.bignum_inc(n &Number)
fn C.bignum_dec(n &Number)
fn C.bignum_pow( a &Number, b &Number, c &Number) // c = a ^ b
fn C.bignum_isqrt( a &Number, b &Number) // b = integer_square_root_of(a)
fn C.bignum_assign( dst &Number, src &Number) // copy src number to dst number

////////////////////////////////////////////////////////////
// conversion actions to/from big numbers:
pub fn new_bignum() Number {
	return Number{}
}
pub fn from_int(i int) Number {
	n := Number{}
	C.bignum_from_int( &n, i)
	return n
}

pub fn from_u64(u u64) Number {
	n := Number{}
	C.bignum_from_int( &n, u)
	return n
}
pub fn from_string(s string) Number {
	n := Number{}
	C.bignum_from_string(&n, s.str, s.len)
	return n
}

pub fn (n Number) int() int {
	r := C.bignum_to_int(&n)
	return r
}

pub fn (n Number) str() string {
	// TODO: return a decimal representation of the bignumber n.
	// A decimal representation will be easier to use in the repl
	// but will be slower to calculate. Also, it is not implemented
	// in the bn library.
	return 'Number (in hex): ' + n.hexstr()
}

pub fn (n Number) hexstr() string {
	mut buf := [STRING_BUFFER_SIZE]byte
	C.bignum_to_string( &n, buf, STRING_BUFFER_SIZE)
	// NB: bignum_to_string , returns the HEXADECIMAL representation of the bignum n
	s := tos_clone( buf )
	if s.len == 0 { return '0' }
	return s
}
////////////////////////////////////////////////////////////
// overloaded ops for the numbers:
pub fn (a Number) + (b Number) Number {
	c := Number{}
	C.bignum_add(&a, &b, &c)
	return c
}

pub fn (a Number) - (b Number) Number {
	c := Number{}
	C.bignum_sub(&a, &b, &c)
	return c
}

pub fn (a Number) * (b Number) Number {
	c := Number{}
	C.bignum_mul(&a, &b, &c)
	return c
}

pub fn (a Number) / (b Number) Number {
	c := Number{}
	C.bignum_div(&a, &b, &c)
	return c
}

pub fn (a Number) % (b Number) Number {
	c := Number{}
	C.bignum_mod(&a, &b, &c)
	return c
}

pub fn divmod( a &Number, b &Number, c &Number) Number {
	d := Number{}
	C.bignum_divmod( a, b, c, &d)
	return d
}
////////////////////////////////////////////////////////////
pub fn cmp(a Number, b Number) int {
	return C.bignum_cmp(&a,&b)
}
pub fn (a Number) is_zero() bool {
	return int(C.bignum_is_zero(&a)) != 0
}
pub fn (a mut Number) inc() {
	C.bignum_inc(a)
}
pub fn (a mut Number) dec() {
	C.bignum_dec(a)
}
pub fn pow(a Number, b Number) Number {
	c := Number{}
	C.bignum_pow(&a,&b,&c)
	return c
}
pub fn (a Number) isqrt() Number {
	b := Number{}
	C.bignum_isqrt(&a,&b)
	return b
}
////////////////////////////////////////////////////////////
pub fn b_and(a Number, b Number) Number {
	c := Number{}
	C.bignum_and(&a,&b,&c)
	return c
}
pub fn b_or(a Number, b Number) Number {
	c := Number{}
	C.bignum_or(&a,&b,&c)
	return c
}
pub fn b_xor(a Number, b Number) Number {
	c := Number{}
	C.bignum_xor(&a,&b,&c)
	return c
}
pub fn (a Number) lshift(nbits int) Number {
	b := Number{}
	C.bignum_lshift(&a,&b,nbits)
	return b
}
pub fn (a Number) rshift(nbits int) Number {
	b := Number{}
	C.bignum_rshift(&a,&b,nbits)
	return b
}
pub fn (a Number) clone() Number {
	b := Number{}
	C.bignum_assign(&b,&a)
	return b
}
////////////////////////////////////////////////////////////
pub fn factorial(nn Number) Number {
	mut n := nn.clone()
	mut a := nn.clone()
	n.dec()
	mut i:=1
	for !n.is_zero() {
		res := a * n
		n.dec()
		a = res
		i++
	}
	return a
}

pub fn fact(n int) Number {
	return factorial( bignum.from_int(n) )
}