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std.bigint: support construction from Int128 #10948

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std.bigint: support construction from Int128 #10948

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b93da13
std.bigint: addedBigInt constructor for Int128
Prashant-900 Feb 9, 2026
a975c61
add comment before public constructor.
Prashant-900 Feb 9, 2026
96d4e79
included the opAssign for assignment from int128 ans unittest for san…
Prashant-900 Feb 10, 2026
26b5167
style fixed
Prashant-900 Feb 10, 2026
8cd3fe9
b = BigInt(x); to b = x; conversion
Prashant-900 Feb 10, 2026
7466894
Remove blank line before BigInt constructor
Prashant-900 Mar 11, 2026
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86 changes: 86 additions & 0 deletions std/bigint.d
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,92 @@ public:
opAssign(x);
}

/// Construct `BigInt` from `Int128`
import std.int128 : Int128;
Comment on lines +191 to +192
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@Bolpat Bolpat Jun 3, 2026

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Suggested change
/// Construct `BigInt` from `Int128`
import std.int128 : Int128;
import std.int128 : Int128;
/// Construct `BigInt` from `Int128`

Not sure if this is needed, but I think the doc comment should be after the import.

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@pbackus pbackus Jun 3, 2026

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Putting this import here means that it will be affected by the public: attribute specifier on line 53, turning it into a public import. This means that the symbol Int128 will be visible as BigInt.Int128 from outside the std.bigint module.

To fix this, move the import to the top of the module, outside the declaration of struct BigInt.

this(Int128 x) pure nothrow @safe {
data = data.init;
opAssign(x);
}

/// Assignment from `Int128`.
BigInt opAssign(T : Int128)(T x) @safe
{
sign = false;

ulong lo = x.data.lo;
long hi = x.data.hi;

// Determine sign and get absolute value
if (hi < 0)
{
sign = true;

// Two's complement negate
lo = ~lo + 1;
hi = ~hi + (lo == 0);
}

// Now (hi, lo) is the positive magnitude
if (hi != 0)
{
ulong[2] mag = [cast(ulong) hi, lo];
data.fromMagnitude(mag[]);
}
else
{
data = lo;
}

if (data.isZero)
sign = false;

return this;
}

///
@safe unittest
{
import std.int128;
Int128 x;
BigInt b;
BigInt re;

x = Int128(0L);
b = x;
re = BigInt(0L);
assert(b == re);

x = Int128(42L);
b = x;
re = BigInt(42L);
assert(b == re);

x = Int128(-42L);
b = x;
re = BigInt(-42L);
assert(b == re);

x = Int128(-1L);
b = x;
re = BigInt(-1L);
assert(b == re);

x = (Int128(1L) << 100) + Int128(12345L);
b = x;
re = (BigInt(1L) << 100) + BigInt(12345L);
assert(b == re);

x = -((Int128(1L) << 100) + Int128(12345L));
b = x;
re = -((BigInt(1L) << 100) + BigInt(12345L));
assert(b == re);

x = Int128.min;
b = x;
re = -(BigInt(1L) << 127);
assert(b == re);
}

///
@safe unittest
{
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