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bit: Improved bitfield extraction.

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This commit is contained in:
Jeroen van Rijn
2021-08-11 20:59:53 +02:00
parent 85a2a8815e
commit 463003e86a
6 changed files with 158 additions and 102 deletions
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core/math/big/helpers.odin
+33 -61
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@@ -13,6 +13,8 @@ import "core:mem"
import "core:intrinsics"
import rnd "core:math/rand"
// import "core:fmt"
/*
TODO: Int.flags and Constants like ONE, NAN, etc, are not yet properly handled everywhere.
*/
@@ -193,9 +195,7 @@ extract_bit :: proc(a: ^Int, bit_offset: int) -> (bit: DIGIT, err: Error) {
/*
Check that `a`is usable.
*/
if err = clear_if_uninitialized(a); err != nil {
return 0, err;
}
if err = clear_if_uninitialized(a); err != nil { return 0, err; }
limb := bit_offset / _DIGIT_BITS;
if limb < 0 || limb >= a.used {
@@ -207,72 +207,44 @@ extract_bit :: proc(a: ^Int, bit_offset: int) -> (bit: DIGIT, err: Error) {
return 1 if ((a.digit[limb] & i) != 0) else 0, nil;
}
/*
TODO: Optimize.
*/
int_bitfield_extract :: proc(a: ^Int, offset, count: int) -> (res: _WORD, err: Error) {
/*
Check that `a`is usable.
Check that `a` is usable.
*/
if err = clear_if_uninitialized(a); err != nil {
return 0, err;
}
if err = clear_if_uninitialized(a); err != nil { return 0, err; }
if count > _WORD_BITS || count < 1 { return 0, .Invalid_Argument; }
if count > _WORD_BITS || count < 1 {
return 0, .Invalid_Argument;
}
for shift := 0; shift < count; shift += 1 {
bit_offset := offset + shift;
when true {
v: DIGIT;
e: Error;
limb := bit_offset / _DIGIT_BITS;
mask := DIGIT(1 << DIGIT((bit_offset % _DIGIT_BITS)));
for shift := 0; shift < count; shift += 1 {
o := offset + shift;
v, e = extract_bit(a, o);
if e != nil {
break;
}
res = res + _WORD(v) << uint(shift);
if (a.digit[limb] & mask) != 0 {
res += _WORD(1) << uint(shift);
}
return res, e;
} else {
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;
}
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, nil;
}
return res, nil;
}
int_bitfield_extract_fast :: proc(a: ^Int, offset, count: int) -> (res: _WORD, err: Error) {
/*
Check that `a` is usable.
*/
if err = clear_if_uninitialized(a); err != nil { return 0, err; }
if count > _WORD_BITS || count < 1 { return 0, .Invalid_Argument; }
for shift := 0; shift < count; shift += 1 {
bit_offset := offset + shift;
limb := bit_offset / _DIGIT_BITS;
mask := DIGIT(1 << DIGIT((bit_offset % _DIGIT_BITS)));
if (a.digit[limb] & mask) != 0 {
res += _WORD(1) << uint(shift);
}
}
return res, nil;
}
/*