ARM 学习笔记之5： Shift operations (LSL)

Logical shift left (LSL)

Logical shift left by n bits moves the right-hand 32-n bits of a register to the left by n places, into the lefthand 32-n bits of the result. It sets the right-hand n bits of the result to 0.
You can use the LSL #n operation to multiply the value in the register Rm by 2n, if the value is regarded
as an unsigned integer or a two’s complement signed integer. Overflow can occur without warning.
When the instruction is LSLS or when LSL #n, with non-zero n, is used in Operand2 with the instructions
MOVS, MVNS, ANDS, ORRS, ORNS, EORS, BICS, TEQ or TST, the carry flag is updated to the last bit shifted out,
bit[32-n], of the register Rm. These instructions do not affect the carry flag when used with LSL #0.
--------------------------------------- Note --------------------------------------------
• If n is 32 or more, then all the bits in the result are cleared to 0.
• If n is 33 or more and the carry flag is updated, it is updated to 0.
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