shiftRight
r = a >> shift r and a may alias.
Asserts there is enough memory to fit the result. The upper bound Limb count is
a.limbs.len - (shift / (@bitSizeOf(Limb))).
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 shiftRight(r: *Mutable, a: Const, shift: usize) void {
const full_limbs_shifted_out = shift / limb_bits;
const remaining_bits_shifted_out = shift % limb_bits;
if (a.limbs.len <= full_limbs_shifted_out) {
// Shifting negative numbers converges to -1 instead of 0
if (a.positive) {
r.len = 1;
r.positive = true;
r.limbs[0] = 0;
} else {
r.len = 1;
r.positive = false;
r.limbs[0] = 1;
}
return;
}
const nonzero_negative_shiftout = if (a.positive) false else nonzero: {
for (a.limbs[0..full_limbs_shifted_out]) |x| {
if (x != 0)
break :nonzero true;
}
if (remaining_bits_shifted_out == 0)
break :nonzero false;
const not_covered: Log2Limb = @intCast(limb_bits - remaining_bits_shifted_out);
break :nonzero a.limbs[full_limbs_shifted_out] << not_covered != 0;
};
const new_len = llshr(r.limbs, a.limbs, shift);
r.len = new_len;
r.positive = a.positive;
if (nonzero_negative_shiftout) r.addScalar(r.toConst(), -1);
r.normalize(r.len);
}