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bigint: Add count_bits and more prep.

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This commit is contained in:
Jeroen van Rijn
2021-07-17 01:04:27 +02:00
parent dfd5a993a2
commit 905d5459a9
4 changed files with 41 additions and 20 deletions
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1
core/math/bigint/basic.odin
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@@ -89,7 +89,6 @@ add_digit :: proc(dest, a: ^Int, digit: DIGIT) -> (err: Error) {
If `a` is negative and `|a|` >= `digit`, call `dest = |a| - digit`
*/
if is_neg(a) && (a.used > 1 || a.digit[0] >= digit) {
fmt.print("a = neg, %v\n", print_int(a));
/*
Temporarily fix `a`'s sign.
*/

31
core/math/bigint/bigint.odin
View File

@@ -9,6 +9,8 @@ package bigint
The code started out as an idiomatic source port of libTomMath, which is in the public domain, with thanks.
*/
import "core:intrinsics"
/*
Tunables
*/
@@ -97,26 +99,23 @@ when size_of(rawptr) == 8 {
/*
We can use u128 as an intermediary.
*/
DIGIT :: distinct(u64);
_DIGIT_BITS :: 60;
_WORD :: u128;
_MAX_COMBA :: 1 << (128 - (2 * _DIGIT_BITS)) ;
_WARRAY :: 1 << ((128 - (2 * _DIGIT_BITS)) + 1);
DIGIT :: distinct(u64);
_WORD :: distinct(u128);
} else {
DIGIT :: distinct(u32);
_DIGIT_BITS :: 28;
_WORD :: u64;
_MAX_COMBA :: 1 << ( 64 - (2 * _DIGIT_BITS)) ;
_WARRAY :: 1 << (( 64 - (2 * _DIGIT_BITS)) + 1);
DIGIT :: distinct(u32);
_WORD :: distinct(u64);
}
#assert(size_of(_WORD) == 2 * size_of(DIGIT));
_MASK :: (DIGIT(1) << DIGIT(_DIGIT_BITS)) - DIGIT(1);
_DIGIT_MAX :: _MASK;
_BITS_IN_BYTE :: 8;
_BITS_IN_TYPE :: #force_inline proc($T) -> int where intrinsics.type_is_integer(T) {
return _BITS_IN_BYTE * size_of(T);
}
_DIGIT_TYPE_BITS :: 8 * size_of(DIGIT);
_WORD_TYPE_BITS :: 8 * size_of(_WORD);
_DIGIT_BITS :: _DIGIT_TYPE_BITS - 4;
_MASK :: (DIGIT(1) << DIGIT(_DIGIT_BITS)) - DIGIT(1);
_DIGIT_MAX :: _MASK;
_MAX_COMBA :: 1 << (_WORD_TYPE_BITS - (2 * _DIGIT_BITS)) ;
_WARRAY :: 1 << ((_WORD_TYPE_BITS - (2 * _DIGIT_BITS)) + 1);
Order :: enum i8 {
LSB_First = -1,

6
core/math/bigint/example.odin
View File

@@ -75,9 +75,9 @@ demo :: proc() {
err = sub(c, a, b);
// err = add(c, a, b);
fmt.printf("Error: %v\n", err);
fmt.printf("a: %v\n", print_int(a));
fmt.printf("b: %v\n", print_int(b));
fmt.printf("c: %v\n", print_int(c));
fmt.printf("a: %v, bits: %v\n", print_int(a), count_bits(a));
fmt.printf("b: %v, bits: %v\n", print_int(b), count_bits(b));
fmt.printf("c: %v, bits: %v\n", print_int(c), count_bits(c));
}
main :: proc() {

23
core/math/bigint/helpers.odin
View File

@@ -217,6 +217,29 @@ minus_one :: proc(a: ^Int, minimize := false) -> (err: Error) {
return .OK;
}
/*
Count bits in an `Int`.
*/
count_bits :: proc(a: ^Int) -> (count: int) {
assert_initialized(a);
/*
Fast path for zero.
*/
if is_zero(a) {
return 0;
}
/*
Get the number of DIGITs and use it.
*/
count = (a.used - 1) * _DIGIT_BITS;
/*
Take the last DIGIT and count the bits in it.
*/
clz := int(intrinsics.count_leading_zeros(a.digit[a.used - 1]));
count += (_DIGIT_TYPE_BITS - clz);
return;
}
/*
Internal helpers.
*/