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big: Improve int_bitfield_extract.

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Jeroen van Rijn
2021-08-11 20:59:51 +02:00
parent 9c150381bf
commit 2fbff25a18
3 changed files with 78 additions and 29 deletions
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core/math/big/helpers.odin
+38 -19
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@@ -11,7 +11,7 @@ package big
import "core:mem"
import "core:intrinsics"
import "core:math/rand"
import rnd "core:math/rand"
/*
Deallocates the backing memory of one or more `Int`s.
@@ -177,7 +177,7 @@ neg :: proc(dest, src: ^Int, allocator := context.allocator) -> (err: Error) {
/*
Helpers to extract values from the `Int`.
*/
extract_bit :: proc(a: ^Int, bit_offset: int) -> (bit: DIGIT, err: Error) {
int_extract_bit :: proc(a: ^Int, bit_offset: int) -> (bit: DIGIT, err: Error) {
/*
Check that `a`is usable.
*/
@@ -195,10 +195,7 @@ extract_bit :: proc(a: ^Int, bit_offset: int) -> (bit: DIGIT, err: Error) {
return 1 if ((a.digit[limb] & i) != 0) else 0, .None;
}
/*
TODO: Optimize.
*/
extract_bits :: proc(a: ^Int, offset, count: int) -> (res: _WORD, err: Error) {
int_bitfield_extract :: proc(a: ^Int, offset, count: int) -> (res: _WORD, err: Error) {
/*
Check that `a`is usable.
*/
@@ -210,18 +207,40 @@ extract_bits :: proc(a: ^Int, offset, count: int) -> (res: _WORD, err: Error) {
return 0, .Invalid_Argument;
}
v: DIGIT;
e: Error;
for shift := 0; shift < count; shift += 1 {
o := offset + shift;
v, e = extract_bit(a, o);
if e != .None {
break;
}
res = res + _WORD(v) << uint(shift);
limb_lo := offset / _DIGIT_BITS;
bits_lo := offset % _DIGIT_BITS;
limb_hi := (offset + count) / _DIGIT_BITS;
bits_hi := (offset + count) % _DIGIT_BITS;
if limb_lo < 0 || limb_lo >= a.used || limb_hi < 0 || limb_hi >= a.used {
return 0, .Invalid_Argument;
}
return res, e;
for i := limb_hi; i >= limb_lo; i -= 1 {
res <<= _DIGIT_BITS;
/*
Determine which bits to extract from each DIGIT. The whole DIGIT's worth by default.
*/
bit_count := _DIGIT_BITS;
bit_offset := 0;
if i == limb_lo {
bit_count -= bits_lo;
bit_offset = _DIGIT_BITS - bit_count;
} else if i == limb_hi {
bit_count = bits_hi;
bit_offset = 0;
}
d := a.digit[i];
v := (d >> uint(bit_offset)) & DIGIT(1 << uint(bit_count - 1));
m := DIGIT(1 << uint(bit_count-1));
r := v & m;
res |= _WORD(r);
}
return res, .None;
}
/*
@@ -507,9 +526,9 @@ count_lsb :: proc(a: ^Int) -> (count: int, err: Error) {
return count, .None;
}
int_random_digit :: proc(r: ^rand.Rand = nil) -> (res: DIGIT) {
int_random_digit :: proc(r: ^rnd.Rand = nil) -> (res: DIGIT) {
when _DIGIT_BITS == 60 { // DIGIT = u64
return DIGIT(rand.uint64(r)) & _MASK;
return DIGIT(rnd.uint64(r)) & _MASK;
} else when _DIGIT_BITS == 28 { // DIGIT = u32
return DIGIT(rand.uint32(r)) & _MASK;
} else {
@@ -519,7 +538,7 @@ int_random_digit :: proc(r: ^rand.Rand = nil) -> (res: DIGIT) {
return 0; // We shouldn't get here.
}
int_rand :: proc(dest: ^Int, bits: int, r: ^rand.Rand = nil) -> (err: Error) {
int_rand :: proc(dest: ^Int, bits: int, r: ^rnd.Rand = nil) -> (err: Error) {
bits := bits;
if bits <= 0 { return .Invalid_Argument; }