Module bit32

This library provides bitwise operations.

The library is taken from Lua 5.2, and this documentation also reuses Lua 5.2 Bitwise Operations documentation.

Unless otherwise stated, all functions accept numeric arguments in the range (-251,+251); each argument is normalized to the remainder of its division by 232 and truncated to an integer (in some unspecified way), so that its final value falls in the range [0,232 - 1]. Similarly, all results are in the range [0,232 - 1]. Note that bit32.bnot(0) is 0xFFFFFFFF, which is different from -1.

Type bit32

bit32.arshift(x, disp)	Returns the number x shifted disp bits to the right.
bit32.band(...)	Returns the bitwise and of its operands.
bit32.bnot(x)	Returns the bitwise negation of x.
bit32.bor(...)	Returns the bitwise or of its operands.
bit32.btest(...)	Returns a boolean signaling whether the bitwise and of its operands is different from zero.
bit32.bxor(...)	Returns the bitwise exclusive or of its operands.
bit32.extract(n, field, width)	Returns the unsigned number formed by the bits field to field + width - 1 from n.
bit32.lrotate(x, disp)	Returns the number x rotated disp bits to the left.
bit32.lshift(x, disp)	Returns the number x shifted disp bits to the left.
bit32.replace(n, v, field, width)	Returns a copy of n with the bits field to field + width - 1 replaced by the value v.
bit32.rrotate(x, disp)	Returns the number x rotated disp bits to the right.
bit32.rshift(x, disp)	Returns the number x shifted disp bits to the right.

Type bit32

Field(s)

bit32.arshift(x, disp)

Returns the number x shifted disp bits to the right.

The number disp may be any representable integer. Negative displacements shift to the left. This shift operation is what is called arithmetic shift. Vacant bits on the left are filled with copies of the higher bit of x; vacant bits on the right are filled with zeros. In particular, displacements with absolute values higher than 31 result in zero or 0xFFFFFFFF (all original bits are shifted out).

Parameters

• x : the number that will be shifted

• disp : the number of bits to be shifted to the right

Return value

the number resulting of the operation.

Usage:

bit32.arshift(0x00F0000F, 2) --> 0x3C0003

bit32.band(...)

Returns the bitwise and of its operands.

Parameter

• ... : variable number of arguments to operate the bitwise and on, each argument must be a number.

Return value

the number resulting of the operation.

Usage:

bit32.band(0xAFF, 0xFAF, 0xFFA)  --> 0xAAA

bit32.bnot(x)

Returns the bitwise negation of x.

For any integer x, the following identity holds:

  assert(bit32.bnot(x) == (-1 - x) % 2^32)

Parameter

• x : number to return the bitwise negation of.

Return value

the number resulting of the operation.

Usage:

bit32.bnot(0x00F0000F)  --> 0xFF0FFFF0

bit32.bor(...)

Returns the bitwise or of its operands.

Parameter

• ... : variable number of arguments to operate the bitwise or on, each argument must be a number.

Return value

the number resulting of the operation.

Usage:

bit32.bor(0xA, 0xA0, 0xA00)  --> 0xAAA

bit32.btest(...)

Returns a boolean signaling whether the bitwise and of its operands is different from zero.

Parameter

• ... : variable number of arguments to test, each argument must be a number.

Return value

a boolean signaling whether the bitwise and of the operands is different from zero.

Usages:

• bit32.btest(42, 1)  --> false

• bit32.btest(43, 1)  --> true

bit32.bxor(...)

Returns the bitwise exclusive or of its operands.

Parameter

• ... : variable number of arguments to operate the bitwise exclusive or on , each argument must be a number.

Return value

the number resulting of the operation.

Usage:

bit32.bxor(0, 0xBBB, 0)  --> 0xBBB

bit32.extract(n, field, width)

Returns the unsigned number formed by the bits field to field + width - 1 from n.

Bits are numbered from 0 (least significant) to 31 (most significant). All accessed bits must be in the range [0, 31]. The default for width is 1.

Parameters

• n : the number to extract bits from

• field : the first bit to extract

• width : optional number, number of bits to extract

Return value

the unsigned number resulting of the operation.

Usage:

bit32.extract(0xFEA8C523, 8, 8)  --> 0xC5

bit32.lrotate(x, disp)

Returns the number x rotated disp bits to the left.

The number disp may be any representable integer. For any valid displacement, the following identity holds:

assert(bit32.lrotate(x, disp) == bit32.lrotate(x, disp % 32))

In particular, negative displacements rotate to the right.

Parameters

• x : the number that will be rotated

• disp : the number of bits to be rotated

Return value

the number resulting of the operation.

Usage:

bit32.lrotate(0x12345678, 8)  --> 0x34567812

bit32.lshift(x, disp)

Returns the number x shifted disp bits to the left.

The number disp may be any representable integer. Negative displacements shift to the right. In any direction, vacant bits are filled with zeros. In particular, displacements with absolute values higher than 31 result in zero (all bits are shifted out).

For positive displacements, the following equality holds:

assert(bit32.lshift(b, disp) == (b * 2^disp) % 2^32)

Parameters

• x : the number that will be shifted

• disp : the number of bits to be shifted

Return value

the number resulting of the operation.

Usage:

bit32.lshift(0x12345678, 8)  --> 0x34567800

bit32.replace(n, v, field, width)

Returns a copy of n with the bits field to field + width - 1 replaced by the value v.

See bit32.extract for details about field and width.

Parameters

• n : the number to replace bits in.

• v : the value used to replace bits in n.

• field : the first bit to replace

• width : optional number, number of bits to replace

Return value

the number resulting of the operation.

Usage:

bit32.replace(0xFEA8C523, 0x42, 8, 8)  --> 0xFEA84223

bit32.rrotate(x, disp)

Returns the number x rotated disp bits to the right.

The number disp may be any representable integer. For any valid displacement, the following identity holds:

assert(bit32.rrotate(x, disp) == bit32.rrotate(x, disp % 32))

In particular, negative displacements rotate to the left.

Parameters

• x : the number that will be rotated

• disp : the number of bits to be rotated

Return value

the number resulting of the operation.

bit32.rshift(x, disp)

Returns the number x shifted disp bits to the right.

The number disp may be any representable integer. Negative displacements shift to the left. In any direction, vacant bits are filled with zeros. In particular, displacements with absolute values higher than 31 result in zero (all bits are shifted out).

For positive displacements, the following equality holds:

assert(bit32.rshift(b, disp) == math.floor(b % 2^32 / 2^disp))

This shift operation is what is called logical shift.

Parameters

• x : the number that will be shifted

• disp : the number of bits to be shifted to the right

Return value

the number resulting of the operation.

Usage:

bit32.rshift(0x12345678, 8)  --> 0x123456