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Odin/core/math/big/private.odin
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Jeroen van Rijn 2b274fefbb big: Add _private_int_sqr_karatsuba.
2021-08-11 20:59:54 +02:00

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package big
/*
Copyright 2021 Jeroen van Rijn <nom@duclavier.com>.
Made available under Odin's BSD-2 license.
An arbitrary precision mathematics implementation in Odin.
For the theoretical underpinnings, see Knuth's The Art of Computer Programming, Volume 2, section 4.3.
The code started out as an idiomatic source port of libTomMath, which is in the public domain, with thanks.
============================= Private procedures =============================
Private procedures used by the above low-level routines follow.
Don't call these yourself unless you really know what you're doing.
They include implementations that are optimimal for certain ranges of input only.
These aren't exported for the same reasons.
*/
import "core:intrinsics"
import "core:mem"
/*
Multiplies |a| * |b| and only computes upto digs digits of result.
HAC pp. 595, Algorithm 14.12 Modified so you can control how
many digits of output are created.
*/
_private_int_mul :: proc(dest, a, b: ^Int, digits: int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
/*
Can we use the fast multiplier?
*/
if digits < _WARRAY && min(a.used, b.used) < _MAX_COMBA {
return #force_inline _private_int_mul_comba(dest, a, b, digits);
}
/*
Set up temporary output `Int`, which we'll swap for `dest` when done.
*/
t := &Int{};
if err = internal_grow(t, max(digits, _DEFAULT_DIGIT_COUNT)); err != nil { return err; }
t.used = digits;
/*
Compute the digits of the product directly.
*/
pa := a.used;
for ix := 0; ix < pa; ix += 1 {
/*
Limit ourselves to `digits` DIGITs of output.
*/
pb := min(b.used, digits - ix);
carry := _WORD(0);
iy := 0;
/*
Compute the column of the output and propagate the carry.
*/
#no_bounds_check for iy = 0; iy < pb; iy += 1 {
/*
Compute the column as a _WORD.
*/
column := _WORD(t.digit[ix + iy]) + _WORD(a.digit[ix]) * _WORD(b.digit[iy]) + carry;
/*
The new column is the lower part of the result.
*/
t.digit[ix + iy] = DIGIT(column & _WORD(_MASK));
/*
Get the carry word from the result.
*/
carry = column >> _DIGIT_BITS;
}
/*
Set carry if it is placed below digits
*/
if ix + iy < digits {
t.digit[ix + pb] = DIGIT(carry);
}
}
internal_swap(dest, t);
internal_destroy(t);
return internal_clamp(dest);
}
/*
Fast (comba) multiplier
This is the fast column-array [comba] multiplier. It is
designed to compute the columns of the product first
then handle the carries afterwards. This has the effect
of making the nested loops that compute the columns very
simple and schedulable on super-scalar processors.
This has been modified to produce a variable number of
digits of output so if say only a half-product is required
you don't have to compute the upper half (a feature
required for fast Barrett reduction).
Based on Algorithm 14.12 on pp.595 of HAC.
*/
_private_int_mul_comba :: proc(dest, a, b: ^Int, digits: int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
/*
Set up array.
*/
W: [_WARRAY]DIGIT = ---;
/*
Grow the destination as required.
*/
if err = internal_grow(dest, digits); err != nil { return err; }
/*
Number of output digits to produce.
*/
pa := min(digits, a.used + b.used);
/*
Clear the carry
*/
_W := _WORD(0);
ix: int;
for ix = 0; ix < pa; ix += 1 {
tx, ty, iy, iz: int;
/*
Get offsets into the two bignums.
*/
ty = min(b.used - 1, ix);
tx = ix - ty;
/*
This is the number of times the loop will iterate, essentially.
while (tx++ < a->used && ty-- >= 0) { ... }
*/
iy = min(a.used - tx, ty + 1);
/*
Execute loop.
*/
#no_bounds_check for iz = 0; iz < iy; iz += 1 {
_W += _WORD(a.digit[tx + iz]) * _WORD(b.digit[ty - iz]);
}
/*
Store term.
*/
W[ix] = DIGIT(_W) & _MASK;
/*
Make next carry.
*/
_W = _W >> _WORD(_DIGIT_BITS);
}
/*
Setup dest.
*/
old_used := dest.used;
dest.used = pa;
/*
Now extract the previous digit [below the carry].
*/
copy_slice(dest.digit[0:], W[:pa]);
/*
Clear unused digits [that existed in the old copy of dest].
*/
internal_zero_unused(dest, old_used);
/*
Adjust dest.used based on leading zeroes.
*/
return internal_clamp(dest);
}
/*
Low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16
Assumes `dest` and `src` to not be `nil`, and `src` to have been initialized.
*/
_private_int_sqr :: proc(dest, src: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
pa := src.used;
t := &Int{}; ix, iy: int;
/*
Grow `t` to maximum needed size, or `_DEFAULT_DIGIT_COUNT`, whichever is bigger.
*/
if err = internal_grow(t, max((2 * pa) + 1, _DEFAULT_DIGIT_COUNT)); err != nil { return err; }
t.used = (2 * pa) + 1;
#no_bounds_check for ix = 0; ix < pa; ix += 1 {
carry := DIGIT(0);
/*
First calculate the digit at 2*ix; calculate double precision result.
*/
r := _WORD(t.digit[ix+ix]) + (_WORD(src.digit[ix]) * _WORD(src.digit[ix]));
/*
Store lower part in result.
*/
t.digit[ix+ix] = DIGIT(r & _WORD(_MASK));
/*
Get the carry.
*/
carry = DIGIT(r >> _DIGIT_BITS);
#no_bounds_check for iy = ix + 1; iy < pa; iy += 1 {
/*
First calculate the product.
*/
r = _WORD(src.digit[ix]) * _WORD(src.digit[iy]);
/* Now calculate the double precision result. Nóte we use
* addition instead of *2 since it's easier to optimize
*/
r = _WORD(t.digit[ix+iy]) + r + r + _WORD(carry);
/*
Store lower part.
*/
t.digit[ix+iy] = DIGIT(r & _WORD(_MASK));
/*
Get carry.
*/
carry = DIGIT(r >> _DIGIT_BITS);
}
/*
Propagate upwards.
*/
#no_bounds_check for carry != 0 {
r = _WORD(t.digit[ix+iy]) + _WORD(carry);
t.digit[ix+iy] = DIGIT(r & _WORD(_MASK));
carry = DIGIT(r >> _WORD(_DIGIT_BITS));
iy += 1;
}
}
err = internal_clamp(t);
internal_swap(dest, t);
internal_destroy(t);
return err;
}
/*
The jist of squaring...
You do like mult except the offset of the tmpx [one that starts closer to zero] can't equal the offset of tmpy.
So basically you set up iy like before then you min it with (ty-tx) so that it never happens.
You double all those you add in the inner loop. After that loop you do the squares and add them in.
Assumes `dest` and `src` not to be `nil` and `src` to have been initialized.
*/
_private_int_sqr_comba :: proc(dest, src: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
W: [_WARRAY]DIGIT = ---;
/*
Grow the destination as required.
*/
pa := uint(src.used) + uint(src.used);
if err = internal_grow(dest, int(pa)); err != nil { return err; }
/*
Number of output digits to produce.
*/
W1 := _WORD(0);
_W : _WORD = ---;
ix := uint(0);
#no_bounds_check for ; ix < pa; ix += 1 {
/*
Clear counter.
*/
_W = {};
/*
Get offsets into the two bignums.
*/
ty := min(uint(src.used) - 1, ix);
tx := ix - ty;
/*
This is the number of times the loop will iterate,
essentially while (tx++ < a->used && ty-- >= 0) { ... }
*/
iy := min(uint(src.used) - tx, ty + 1);
/*
Now for squaring, tx can never equal ty.
We halve the distance since they approach at a rate of 2x,
and we have to round because odd cases need to be executed.
*/
iy = min(iy, ((ty - tx) + 1) >> 1 );
/*
Execute loop.
*/
#no_bounds_check for iz := uint(0); iz < iy; iz += 1 {
_W += _WORD(src.digit[tx + iz]) * _WORD(src.digit[ty - iz]);
}
/*
Double the inner product and add carry.
*/
_W = _W + _W + W1;
/*
Even columns have the square term in them.
*/
if ix & 1 == 0 {
_W += _WORD(src.digit[ix >> 1]) * _WORD(src.digit[ix >> 1]);
}
/*
Store it.
*/
W[ix] = DIGIT(_W & _WORD(_MASK));
/*
Make next carry.
*/
W1 = _W >> _DIGIT_BITS;
}
/*
Setup dest.
*/
old_used := dest.used;
dest.used = src.used + src.used;
#no_bounds_check for ix = 0; ix < pa; ix += 1 {
dest.digit[ix] = W[ix] & _MASK;
}
/*
Clear unused digits [that existed in the old copy of dest].
*/
internal_zero_unused(dest, old_used);
return internal_clamp(dest);
}
/*
Karatsuba squaring, computes `dest` = `src` * `src` using three half-size squarings.
See comments of `_private_int_mul_karatsuba` for details.
It is essentially the same algorithm but merely tuned to perform recursive squarings.
*/
_private_int_sqr_karatsuba :: proc(dest, src: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
x0, x1, t1, t2, x0x0, x1x1 := &Int{}, &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
defer internal_destroy(x0, x1, t1, t2, x0x0, x1x1);
/*
Min # of digits, divided by two.
*/
B := src.used >> 1;
/*
Init temps.
*/
if err = internal_grow(x0, B); err != nil { return err; }
if err = internal_grow(x1, src.used - B); err != nil { return err; }
if err = internal_grow(t1, src.used * 2); err != nil { return err; }
if err = internal_grow(t2, src.used * 2); err != nil { return err; }
if err = internal_grow(x0x0, B * 2 ); err != nil { return err; }
if err = internal_grow(x1x1, (src.used - B) * 2); err != nil { return err; }
/*
Now shift the digits.
*/
x0.used = B;
x1.used = src.used - B;
internal_copy_digits(x0, src, x0.used);
#force_inline mem.copy_non_overlapping(&x1.digit[0], &src.digit[B], size_of(DIGIT) * x1.used);
internal_clamp(x0);
/*
Now calc the products x0*x0 and x1*x1.
*/
if err = internal_sqr(x0x0, x0); err != nil { return err; }
if err = internal_sqr(x1x1, x1); err != nil { return err; }
/*
Now calc (x1+x0)^2
*/
if err = internal_add(t1, x0, x1); err != nil { return err; }
if err = internal_sqr(t1, t1); err != nil { return err; }
/*
Add x0y0
*/
if err = internal_add(t2, x0x0, x1x1); err != nil { return err; }
if err = internal_sub(t1, t1, t2); err != nil { return err; }
/*
Shift by B.
*/
if err = internal_shl_digit(t1, B); err != nil { return err; }
if err = internal_shl_digit(x1x1, B * 2); err != nil { return err; }
if err = internal_add(t1, t1, x0x0); err != nil { return err; }
if err = internal_add(dest, t1, x1x1); err != nil { return err; }
return internal_clamp(dest);
}
/*
Divide by three (based on routine from MPI and the GMP manual).
*/
_private_int_div_3 :: proc(quotient, numerator: ^Int, allocator := context.allocator) -> (remainder: DIGIT, err: Error) {
context.allocator = allocator;
/*
b = 2^_DIGIT_BITS / 3
*/
b := _WORD(1) << _WORD(_DIGIT_BITS) / _WORD(3);
q := &Int{};
if err = internal_grow(q, numerator.used); err != nil { return 0, err; }
q.used = numerator.used;
q.sign = numerator.sign;
w, t: _WORD;
#no_bounds_check for ix := numerator.used; ix >= 0; ix -= 1 {
w = (w << _WORD(_DIGIT_BITS)) | _WORD(numerator.digit[ix]);
if w >= 3 {
/*
Multiply w by [1/3].
*/
t = (w * b) >> _WORD(_DIGIT_BITS);
/*
Now subtract 3 * [w/3] from w, to get the remainder.
*/
w -= t+t+t;
/*
Fixup the remainder as required since the optimization is not exact.
*/
for w >= 3 {
t += 1;
w -= 3;
}
} else {
t = 0;
}
q.digit[ix] = DIGIT(t);
}
remainder = DIGIT(w);
/*
[optional] store the quotient.
*/
if quotient != nil {
err = clamp(q);
internal_swap(q, quotient);
}
internal_destroy(q);
return remainder, nil;
}
/*
Signed Integer Division
c*b + d == a [i.e. a/b, c=quotient, d=remainder], HAC pp.598 Algorithm 14.20
Note that the description in HAC is horribly incomplete.
For example, it doesn't consider the case where digits are removed from 'x' in
the inner loop.
It also doesn't consider the case that y has fewer than three digits, etc.
The overall algorithm is as described as 14.20 from HAC but fixed to treat these cases.
*/
_private_int_div_school :: proc(quotient, remainder, numerator, denominator: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
if err = error_if_immutable(quotient, remainder); err != nil { return err; }
q, x, y, t1, t2 := &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
defer internal_destroy(q, x, y, t1, t2);
if err = internal_grow(q, numerator.used + 2); err != nil { return err; }
q.used = numerator.used + 2;
if err = internal_init_multi(t1, t2); err != nil { return err; }
if err = internal_copy(x, numerator); err != nil { return err; }
if err = internal_copy(y, denominator); err != nil { return err; }
/*
Fix the sign.
*/
neg := numerator.sign != denominator.sign;
x.sign = .Zero_or_Positive;
y.sign = .Zero_or_Positive;
/*
Normalize both x and y, ensure that y >= b/2, [b == 2**MP_DIGIT_BIT]
*/
norm := internal_count_bits(y) % _DIGIT_BITS;
if norm < _DIGIT_BITS - 1 {
norm = (_DIGIT_BITS - 1) - norm;
if err = internal_shl(x, x, norm); err != nil { return err; }
if err = internal_shl(y, y, norm); err != nil { return err; }
} else {
norm = 0;
}
/*
Note: HAC does 0 based, so if used==5 then it's 0,1,2,3,4, i.e. use 4
*/
n := x.used - 1;
t := y.used - 1;
/*
while (x >= y*b**n-t) do { q[n-t] += 1; x -= y*b**{n-t} }
y = y*b**{n-t}
*/
if err = internal_shl_digit(y, n - t); err != nil { return err; }
c := internal_cmp(x, y);
for c != -1 {
q.digit[n - t] += 1;
if err = internal_sub(x, x, y); err != nil { return err; }
c = internal_cmp(x, y);
}
/*
Reset y by shifting it back down.
*/
internal_shr_digit(y, n - t);
/*
Step 3. for i from n down to (t + 1).
*/
#no_bounds_check for i := n; i >= (t + 1); i -= 1 {
if (i > x.used) { continue; }
/*
step 3.1 if xi == yt then set q{i-t-1} to b-1, otherwise set q{i-t-1} to (xi*b + x{i-1})/yt
*/
if x.digit[i] == y.digit[t] {
q.digit[(i - t) - 1] = 1 << (_DIGIT_BITS - 1);
} else {
tmp := _WORD(x.digit[i]) << _DIGIT_BITS;
tmp |= _WORD(x.digit[i - 1]);
tmp /= _WORD(y.digit[t]);
if tmp > _WORD(_MASK) {
tmp = _WORD(_MASK);
}
q.digit[(i - t) - 1] = DIGIT(tmp & _WORD(_MASK));
}
/* while (q{i-t-1} * (yt * b + y{t-1})) >
xi * b**2 + xi-1 * b + xi-2
do q{i-t-1} -= 1;
*/
iter := 0;
q.digit[(i - t) - 1] = (q.digit[(i - t) - 1] + 1) & _MASK;
#no_bounds_check for {
q.digit[(i - t) - 1] = (q.digit[(i - t) - 1] - 1) & _MASK;
/*
Find left hand.
*/
internal_zero(t1);
t1.digit[0] = ((t - 1) < 0) ? 0 : y.digit[t - 1];
t1.digit[1] = y.digit[t];
t1.used = 2;
if err = internal_mul(t1, t1, q.digit[(i - t) - 1]); err != nil { return err; }
/*
Find right hand.
*/
t2.digit[0] = ((i - 2) < 0) ? 0 : x.digit[i - 2];
t2.digit[1] = x.digit[i - 1]; /* i >= 1 always holds */
t2.digit[2] = x.digit[i];
t2.used = 3;
if t1_t2 := internal_cmp_mag(t1, t2); t1_t2 != 1 {
break;
}
iter += 1; if iter > 100 { return .Max_Iterations_Reached; }
}
/*
Step 3.3 x = x - q{i-t-1} * y * b**{i-t-1}
*/
if err = int_mul_digit(t1, y, q.digit[(i - t) - 1]); err != nil { return err; }
if err = internal_shl_digit(t1, (i - t) - 1); err != nil { return err; }
if err = internal_sub(x, x, t1); err != nil { return err; }
/*
if x < 0 then { x = x + y*b**{i-t-1}; q{i-t-1} -= 1; }
*/
if x.sign == .Negative {
if err = internal_copy(t1, y); err != nil { return err; }
if err = internal_shl_digit(t1, (i - t) - 1); err != nil { return err; }
if err = internal_add(x, x, t1); err != nil { return err; }
q.digit[(i - t) - 1] = (q.digit[(i - t) - 1] - 1) & _MASK;
}
}
/*
Now q is the quotient and x is the remainder, [which we have to normalize]
Get sign before writing to c.
*/
z, _ := is_zero(x);
x.sign = .Zero_or_Positive if z else numerator.sign;
if quotient != nil {
internal_clamp(q);
internal_swap(q, quotient);
quotient.sign = .Negative if neg else .Zero_or_Positive;
}
if remainder != nil {
if err = internal_shr(x, x, norm); err != nil { return err; }
internal_swap(x, remainder);
}
return nil;
}
/*
Slower bit-bang division... also smaller.
*/
@(deprecated="Use `_int_div_school`, it's 3.5x faster.")
_private_int_div_small :: proc(quotient, remainder, numerator, denominator: ^Int) -> (err: Error) {
ta, tb, tq, q := &Int{}, &Int{}, &Int{}, &Int{};
c: int;
goto_end: for {
if err = internal_one(tq); err != nil { break goto_end; }
num_bits, _ := count_bits(numerator);
den_bits, _ := count_bits(denominator);
n := num_bits - den_bits;
if err = abs(ta, numerator); err != nil { break goto_end; }
if err = abs(tb, denominator); err != nil { break goto_end; }
if err = shl(tb, tb, n); err != nil { break goto_end; }
if err = shl(tq, tq, n); err != nil { break goto_end; }
for n >= 0 {
if c, _ = cmp_mag(ta, tb); c == 0 || c == 1 {
// ta -= tb
if err = sub(ta, ta, tb); err != nil { break goto_end; }
// q += tq
if err = add( q, q, tq); err != nil { break goto_end; }
}
if err = shr1(tb, tb); err != nil { break goto_end; }
if err = shr1(tq, tq); err != nil { break goto_end; }
n -= 1;
}
/*
Now q == quotient and ta == remainder.
*/
neg := numerator.sign != denominator.sign;
if quotient != nil {
swap(quotient, q);
z, _ := is_zero(quotient);
quotient.sign = .Negative if neg && !z else .Zero_or_Positive;
}
if remainder != nil {
swap(remainder, ta);
z, _ := is_zero(numerator);
remainder.sign = .Zero_or_Positive if z else numerator.sign;
}
break goto_end;
}
destroy(ta, tb, tq, q);
return err;
}
/*
Binary split factorial algo due to: http://www.luschny.de/math/factorial/binarysplitfact.html
*/
_private_int_factorial_binary_split :: proc(res: ^Int, n: int, allocator := context.allocator) -> (err: Error) {
inner, outer, start, stop, temp := &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
defer internal_destroy(inner, outer, start, stop, temp);
if err = internal_one(inner, false, allocator); err != nil { return err; }
if err = internal_one(outer, false, allocator); err != nil { return err; }
bits_used := int(_DIGIT_TYPE_BITS - intrinsics.count_leading_zeros(n));
for i := bits_used; i >= 0; i -= 1 {
start := (n >> (uint(i) + 1)) + 1 | 1;
stop := (n >> uint(i)) + 1 | 1;
if err = _private_int_recursive_product(temp, start, stop, 0, allocator); err != nil { return err; }
if err = internal_mul(inner, inner, temp, allocator); err != nil { return err; }
if err = internal_mul(outer, outer, inner, allocator); err != nil { return err; }
}
shift := n - intrinsics.count_ones(n);
return internal_shl(res, outer, int(shift), allocator);
}
/*
Recursive product used by binary split factorial algorithm.
*/
_private_int_recursive_product :: proc(res: ^Int, start, stop: int, level := int(0), allocator := context.allocator) -> (err: Error) {
t1, t2 := &Int{}, &Int{};
defer internal_destroy(t1, t2);
if level > FACTORIAL_BINARY_SPLIT_MAX_RECURSIONS { return .Max_Iterations_Reached; }
num_factors := (stop - start) >> 1;
if num_factors == 2 {
if err = internal_set(t1, start, false, allocator); err != nil { return err; }
when true {
if err = internal_grow(t2, t1.used + 1, false, allocator); err != nil { return err; }
if err = internal_add(t2, t1, 2, allocator); err != nil { return err; }
} else {
if err = add(t2, t1, 2); err != nil { return err; }
}
return internal_mul(res, t1, t2, allocator);
}
if num_factors > 1 {
mid := (start + num_factors) | 1;
if err = _private_int_recursive_product(t1, start, mid, level + 1, allocator); err != nil { return err; }
if err = _private_int_recursive_product(t2, mid, stop, level + 1, allocator); err != nil { return err; }
return internal_mul(res, t1, t2, allocator);
}
if num_factors == 1 { return #force_inline internal_set(res, start, true, allocator); }
return #force_inline internal_one(res, true, allocator);
}
/*
Internal function computing both GCD using the binary method,
and, if target isn't `nil`, also LCM.
Expects the `a` and `b` to have been initialized
and one or both of `res_gcd` or `res_lcm` not to be `nil`.
If both `a` and `b` are zero, return zero.
If either `a` or `b`, return the other one.
The `gcd` and `lcm` wrappers have already done this test,
but `gcd_lcm` wouldn't have, so we still need to perform it.
If neither result is wanted, we have nothing to do.
*/
_private_int_gcd_lcm :: proc(res_gcd, res_lcm, a, b: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
if res_gcd == nil && res_lcm == nil { return nil; }
/*
We need a temporary because `res_gcd` is allowed to be `nil`.
*/
if a.used == 0 && b.used == 0 {
/*
GCD(0, 0) and LCM(0, 0) are both 0.
*/
if res_gcd != nil {
if err = internal_zero(res_gcd); err != nil { return err; }
}
if res_lcm != nil {
if err = internal_zero(res_lcm); err != nil { return err; }
}
return nil;
} else if a.used == 0 {
/*
We can early out with GCD = B and LCM = 0
*/
if res_gcd != nil {
if err = internal_abs(res_gcd, b); err != nil { return err; }
}
if res_lcm != nil {
if err = internal_zero(res_lcm); err != nil { return err; }
}
return nil;
} else if b.used == 0 {
/*
We can early out with GCD = A and LCM = 0
*/
if res_gcd != nil {
if err = internal_abs(res_gcd, a); err != nil { return err; }
}
if res_lcm != nil {
if err = internal_zero(res_lcm); err != nil { return err; }
}
return nil;
}
temp_gcd_res := &Int{};
defer internal_destroy(temp_gcd_res);
/*
If neither `a` or `b` was zero, we need to compute `gcd`.
Get copies of `a` and `b` we can modify.
*/
u, v := &Int{}, &Int{};
defer internal_destroy(u, v);
if err = internal_copy(u, a); err != nil { return err; }
if err = internal_copy(v, b); err != nil { return err; }
/*
Must be positive for the remainder of the algorithm.
*/
u.sign = .Zero_or_Positive; v.sign = .Zero_or_Positive;
/*
B1. Find the common power of two for `u` and `v`.
*/
u_lsb, _ := internal_count_lsb(u);
v_lsb, _ := internal_count_lsb(v);
k := min(u_lsb, v_lsb);
if k > 0 {
/*
Divide the power of two out.
*/
if err = internal_shr(u, u, k); err != nil { return err; }
if err = internal_shr(v, v, k); err != nil { return err; }
}
/*
Divide any remaining factors of two out.
*/
if u_lsb != k {
if err = internal_shr(u, u, u_lsb - k); err != nil { return err; }
}
if v_lsb != k {
if err = internal_shr(v, v, v_lsb - k); err != nil { return err; }
}
for v.used != 0 {
/*
Make sure `v` is the largest.
*/
if internal_cmp_mag(u, v) == 1 {
/*
Swap `u` and `v` to make sure `v` is >= `u`.
*/
internal_swap(u, v);
}
/*
Subtract smallest from largest.
*/
if err = internal_sub(v, v, u); err != nil { return err; }
/*
Divide out all factors of two.
*/
b, _ := internal_count_lsb(v);
if err = internal_shr(v, v, b); err != nil { return err; }
}
/*
Multiply by 2**k which we divided out at the beginning.
*/
if err = internal_shl(temp_gcd_res, u, k); err != nil { return err; }
temp_gcd_res.sign = .Zero_or_Positive;
/*
We've computed `gcd`, either the long way, or because one of the inputs was zero.
If we don't want `lcm`, we're done.
*/
if res_lcm == nil {
internal_swap(temp_gcd_res, res_gcd);
return nil;
}
/*
Computes least common multiple as `|a*b|/gcd(a,b)`
Divide the smallest by the GCD.
*/
if internal_cmp_mag(a, b) == -1 {
/*
Store quotient in `t2` such that `t2 * b` is the LCM.
*/
if err = internal_div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = internal_mul(res_lcm, res_lcm, b);
} else {
/*
Store quotient in `t2` such that `t2 * a` is the LCM.
*/
if err = internal_div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = internal_mul(res_lcm, res_lcm, b);
}
if res_gcd != nil {
internal_swap(temp_gcd_res, res_gcd);
}
/*
Fix the sign to positive and return.
*/
res_lcm.sign = .Zero_or_Positive;
return err;
}
/*
Internal implementation of log.
Assumes `a` not to be `nil` and to have been initialized.
*/
_private_int_log :: proc(a: ^Int, base: DIGIT, allocator := context.allocator) -> (res: int, err: Error) {
bracket_low, bracket_high, bracket_mid, t, bi_base := &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
defer destroy(bracket_low, bracket_high, bracket_mid, t, bi_base);
ic := #force_inline internal_cmp(a, base);
if ic == -1 || ic == 0 {
return 1 if ic == 0 else 0, nil;
}
if err = internal_set(bi_base, base, true, allocator); err != nil { return -1, err; }
if err = internal_clear(bracket_mid, false, allocator); err != nil { return -1, err; }
if err = internal_clear(t, false, allocator); err != nil { return -1, err; }
if err = internal_one(bracket_low, false, allocator); err != nil { return -1, err; }
if err = internal_set(bracket_high, base, false, allocator); err != nil { return -1, err; }
low := 0; high := 1;
/*
A kind of Giant-step/baby-step algorithm.
Idea shamelessly stolen from https://programmingpraxis.com/2010/05/07/integer-logarithms/2/
The effect is asymptotic, hence needs benchmarks to test if the Giant-step should be skipped
for small n.
*/
for {
/*
Iterate until `a` is bracketed between low + high.
*/
if #force_inline internal_cmp(bracket_high, a) != -1 { break; }
low = high;
if err = #force_inline internal_copy(bracket_low, bracket_high); err != nil { return -1, err; }
high <<= 1;
if err = #force_inline internal_sqr(bracket_high, bracket_high); err != nil { return -1, err; }
}
for (high - low) > 1 {
mid := (high + low) >> 1;
if err = #force_inline internal_pow(t, bi_base, mid - low); err != nil { return -1, err; }
if err = #force_inline internal_mul(bracket_mid, bracket_low, t); err != nil { return -1, err; }
mc := #force_inline internal_cmp(a, bracket_mid);
switch mc {
case -1:
high = mid;
internal_swap(bracket_mid, bracket_high);
case 0:
return mid, nil;
case 1:
low = mid;
internal_swap(bracket_mid, bracket_low);
}
}
fc := #force_inline internal_cmp(bracket_high, a);
res = high if fc == 0 else low;
return;
}
/*
Returns the log2 of an `Int`.
Assumes `a` not to be `nil` and to have been initialized.
Also assumes `base` is a power of two.
*/
_private_log_power_of_two :: proc(a: ^Int, base: DIGIT) -> (log: int, err: Error) {
base := base;
y: int;
for y = 0; base & 1 == 0; {
y += 1;
base >>= 1;
}
log = internal_count_bits(a);
return (log - 1) / y, err;
}
/*
Copies DIGITs from `src` to `dest`.
Assumes `src` and `dest` to not be `nil` and have been initialized.
*/
_private_copy_digits :: proc(dest, src: ^Int, digits: int) -> (err: Error) {
digits := digits;
/*
If dest == src, do nothing
*/
if dest == src { return nil; }
digits = min(digits, len(src.digit), len(dest.digit));
mem.copy_non_overlapping(&dest.digit[0], &src.digit[0], size_of(DIGIT) * digits);
return nil;
}
/*
======================== End of private procedures =======================
=============================== Private tables ===============================
Tables used by `internal_*` and `_*`.
*/
_private_prime_table := []DIGIT{
0x0002, 0x0003, 0x0005, 0x0007, 0x000B, 0x000D, 0x0011, 0x0013,
0x0017, 0x001D, 0x001F, 0x0025, 0x0029, 0x002B, 0x002F, 0x0035,
0x003B, 0x003D, 0x0043, 0x0047, 0x0049, 0x004F, 0x0053, 0x0059,
0x0061, 0x0065, 0x0067, 0x006B, 0x006D, 0x0071, 0x007F, 0x0083,
0x0089, 0x008B, 0x0095, 0x0097, 0x009D, 0x00A3, 0x00A7, 0x00AD,
0x00B3, 0x00B5, 0x00BF, 0x00C1, 0x00C5, 0x00C7, 0x00D3, 0x00DF,
0x00E3, 0x00E5, 0x00E9, 0x00EF, 0x00F1, 0x00FB, 0x0101, 0x0107,
0x010D, 0x010F, 0x0115, 0x0119, 0x011B, 0x0125, 0x0133, 0x0137,
0x0139, 0x013D, 0x014B, 0x0151, 0x015B, 0x015D, 0x0161, 0x0167,
0x016F, 0x0175, 0x017B, 0x017F, 0x0185, 0x018D, 0x0191, 0x0199,
0x01A3, 0x01A5, 0x01AF, 0x01B1, 0x01B7, 0x01BB, 0x01C1, 0x01C9,
0x01CD, 0x01CF, 0x01D3, 0x01DF, 0x01E7, 0x01EB, 0x01F3, 0x01F7,
0x01FD, 0x0209, 0x020B, 0x021D, 0x0223, 0x022D, 0x0233, 0x0239,
0x023B, 0x0241, 0x024B, 0x0251, 0x0257, 0x0259, 0x025F, 0x0265,
0x0269, 0x026B, 0x0277, 0x0281, 0x0283, 0x0287, 0x028D, 0x0293,
0x0295, 0x02A1, 0x02A5, 0x02AB, 0x02B3, 0x02BD, 0x02C5, 0x02CF,
0x02D7, 0x02DD, 0x02E3, 0x02E7, 0x02EF, 0x02F5, 0x02F9, 0x0301,
0x0305, 0x0313, 0x031D, 0x0329, 0x032B, 0x0335, 0x0337, 0x033B,
0x033D, 0x0347, 0x0355, 0x0359, 0x035B, 0x035F, 0x036D, 0x0371,
0x0373, 0x0377, 0x038B, 0x038F, 0x0397, 0x03A1, 0x03A9, 0x03AD,
0x03B3, 0x03B9, 0x03C7, 0x03CB, 0x03D1, 0x03D7, 0x03DF, 0x03E5,
0x03F1, 0x03F5, 0x03FB, 0x03FD, 0x0407, 0x0409, 0x040F, 0x0419,
0x041B, 0x0425, 0x0427, 0x042D, 0x043F, 0x0443, 0x0445, 0x0449,
0x044F, 0x0455, 0x045D, 0x0463, 0x0469, 0x047F, 0x0481, 0x048B,
0x0493, 0x049D, 0x04A3, 0x04A9, 0x04B1, 0x04BD, 0x04C1, 0x04C7,
0x04CD, 0x04CF, 0x04D5, 0x04E1, 0x04EB, 0x04FD, 0x04FF, 0x0503,
0x0509, 0x050B, 0x0511, 0x0515, 0x0517, 0x051B, 0x0527, 0x0529,
0x052F, 0x0551, 0x0557, 0x055D, 0x0565, 0x0577, 0x0581, 0x058F,
0x0593, 0x0595, 0x0599, 0x059F, 0x05A7, 0x05AB, 0x05AD, 0x05B3,
0x05BF, 0x05C9, 0x05CB, 0x05CF, 0x05D1, 0x05D5, 0x05DB, 0x05E7,
0x05F3, 0x05FB, 0x0607, 0x060D, 0x0611, 0x0617, 0x061F, 0x0623,
0x062B, 0x062F, 0x063D, 0x0641, 0x0647, 0x0649, 0x064D, 0x0653,
};
when MATH_BIG_FORCE_64_BIT || (!MATH_BIG_FORCE_32_BIT && size_of(rawptr) == 8) {
_factorial_table := [35]_WORD{
/* f(00): */ 1,
/* f(01): */ 1,
/* f(02): */ 2,
/* f(03): */ 6,
/* f(04): */ 24,
/* f(05): */ 120,
/* f(06): */ 720,
/* f(07): */ 5_040,
/* f(08): */ 40_320,
/* f(09): */ 362_880,
/* f(10): */ 3_628_800,
/* f(11): */ 39_916_800,
/* f(12): */ 479_001_600,
/* f(13): */ 6_227_020_800,
/* f(14): */ 87_178_291_200,
/* f(15): */ 1_307_674_368_000,
/* f(16): */ 20_922_789_888_000,
/* f(17): */ 355_687_428_096_000,
/* f(18): */ 6_402_373_705_728_000,
/* f(19): */ 121_645_100_408_832_000,
/* f(20): */ 2_432_902_008_176_640_000,
/* f(21): */ 51_090_942_171_709_440_000,
/* f(22): */ 1_124_000_727_777_607_680_000,
/* f(23): */ 25_852_016_738_884_976_640_000,
/* f(24): */ 620_448_401_733_239_439_360_000,
/* f(25): */ 15_511_210_043_330_985_984_000_000,
/* f(26): */ 403_291_461_126_605_635_584_000_000,
/* f(27): */ 10_888_869_450_418_352_160_768_000_000,
/* f(28): */ 304_888_344_611_713_860_501_504_000_000,
/* f(29): */ 8_841_761_993_739_701_954_543_616_000_000,
/* f(30): */ 265_252_859_812_191_058_636_308_480_000_000,
/* f(31): */ 8_222_838_654_177_922_817_725_562_880_000_000,
/* f(32): */ 263_130_836_933_693_530_167_218_012_160_000_000,
/* f(33): */ 8_683_317_618_811_886_495_518_194_401_280_000_000,
/* f(34): */ 295_232_799_039_604_140_847_618_609_643_520_000_000,
};
} else {
_factorial_table := [21]_WORD{
/* f(00): */ 1,
/* f(01): */ 1,
/* f(02): */ 2,
/* f(03): */ 6,
/* f(04): */ 24,
/* f(05): */ 120,
/* f(06): */ 720,
/* f(07): */ 5_040,
/* f(08): */ 40_320,
/* f(09): */ 362_880,
/* f(10): */ 3_628_800,
/* f(11): */ 39_916_800,
/* f(12): */ 479_001_600,
/* f(13): */ 6_227_020_800,
/* f(14): */ 87_178_291_200,
/* f(15): */ 1_307_674_368_000,
/* f(16): */ 20_922_789_888_000,
/* f(17): */ 355_687_428_096_000,
/* f(18): */ 6_402_373_705_728_000,
/* f(19): */ 121_645_100_408_832_000,
/* f(20): */ 2_432_902_008_176_640_000,
};
};
/*
========================= End of private tables ========================
*/
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