PM0215 datasheet(38/91 Pages) STMICROELECTRONICS

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The STM32 Cortex-M0 instruction set

PM0215

38/91

Doc ID 022979 Rev 1

LSL

Logical shift left by n bits moves the right-hand 32-n bits of the register Rm, to the left by n

places, into the left-hand 32-n bits of the result. And it sets the right-hand n bits of the result

to 0 (see Figure 12: LSL#3 on page 38).

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.

2If n is 33 or more and the carry flag is updated, it is updated to 0.

Figure 12.

LSL#3

ROR

Rotate right by n bits moves the left-hand 32-n bits of the register Rm, to the right by n places,

into the right-hand 32-n bits of the result. It also moves the right-hand n bits of the register

into the left-hand n bits of the result (see Figure 13).

When the instruction is RORS, the carry flag is updated to the last bit rotation, bit[n-1], of the

Note:

If n is 32, then the value of the result is same as the value in Rm, and if the carry flag is

updated, it is updated to bit[31] of Rm.

ROR with shift length, n, more than 32 is the same as ROR with shift length n-32.

Figure 13.

ROR #3

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