DoxigAlpha
std › math › big › int.Mutable › add

add

r = a + b

r, a and b may be aliases.

Asserts the result fits in r. An upper bound on the number of limbs needed by r is @max(a.limbs.len, b.limbs.len) + 1.

Function parameters

Parameters

#
r:*Mutable

Used to indicate either limit of a 2s-complement integer.

Types

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TwosCompIntLimit
Used to indicate either limit of a 2s-complement integer.
Mutable
A arbitrary-precision big integer, with a fixed set of mutable limbs.
Const
A arbitrary-precision big integer, with a fixed set of immutable limbs.
Managed
An arbitrary-precision big integer along with an allocator which manages the memory.

Returns the number of limbs needed to store `scalar`, which must be a

Functions

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calcLimbLen
Returns the number of limbs needed to store `scalar`, which must be a
calcSetStringLimbCount
Assumes `string_len` doesn't account for minus signs if the number is negative.
calcNonZeroTwosCompLimbCount
Compute the number of limbs required to store a 2s-complement number of `bit_count` bits.
calcTwosCompLimbCount
Compute the number of limbs required to store a 2s-complement number of `bit_count` bits.
addMulLimbWithCarry
a + b * c + *carry, sets carry to the overflow bits
llcmp
Returns -1, 0, 1 if |a| < |b|, |a| == |b| or |a| > |b| respectively for limbs.

Source

Implementation

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pub fn add(r: *Mutable, a: Const, b: Const) void {
    if (r.addCarry(a, b)) {
        // Fix up the result. Note that addCarry normalizes by a.limbs.len or b.limbs.len,
        // so we need to set the length here.
        const msl = @max(a.limbs.len, b.limbs.len);
        // `[add|sub]Carry` normalizes by `msl`, so we need to fix up the result manually here.
        // Note, the fact that it normalized means that the intermediary limbs are zero here.
        r.len = msl + 1;
        r.limbs[msl] = 1; // If this panics, there wasn't enough space in `r`.
    }
}