addScalar
r = a + scalar
r and a may be aliases. scalar is a primitive integer type.
Asserts the result fits in r. An upper bound on the number of limbs needed by
r is @max(a.limbs.len, calcLimbLen(scalar)) + 1.
Function parameters
Parameters
Used to indicate either limit of a 2s-complement integer.
Types
- 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
- 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
pub fn addScalar(r: *Mutable, a: Const, scalar: anytype) void {
// Normally we could just determine the number of limbs needed with calcLimbLen,
// but that is not comptime-known when scalar is not a comptime_int. Instead, we
// use calcTwosCompLimbCount for a non-comptime_int scalar, which can be pessimistic
// in the case that scalar happens to be small in magnitude within its type, but it
// is well worth being able to use the stack and not needing an allocator passed in.
// Note that Mutable.init still sets len to calcLimbLen(scalar) in any case.
const limbs_len = comptime switch (@typeInfo(@TypeOf(scalar))) {
.comptime_int => calcLimbLen(scalar),
.int => |info| calcTwosCompLimbCount(info.bits),
else => @compileError("expected scalar to be an int"),
};
var limbs: [limbs_len]Limb = undefined;
const operand = init(&limbs, scalar).toConst();
return add(r, a, operand);
}