How to shift bytes in ARM assembly

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Say I have the following hex values stored in registers;

r1 = #0x1

r2 = #0x2

r3 = #0x3

r4 = #0xA

And I want to store #0x123A in r0.

Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?

asked Nov 11 at 16:58

Ciarán

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up vote
0
down vote

favorite

Say I have the following hex values stored in registers;

r1 = #0x1

r2 = #0x2

r3 = #0x3

r4 = #0xA

And I want to store #0x123A in r0.

Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?

asked Nov 11 at 16:58

Ciarán

add a comment |

up vote
0
down vote

favorite

Say I have the following hex values stored in registers;

r1 = #0x1

r2 = #0x2

r3 = #0x3

r4 = #0xA

And I want to store #0x123A in r0.

Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?

asked Nov 11 at 16:58

Ciarán

Say I have the following hex values stored in registers;

r1 = #0x1

r2 = #0x2

r3 = #0x3

r4 = #0xA

And I want to store #0x123A in r0.

Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?

assembly arm

asked Nov 11 at 16:58

Ciarán

asked Nov 11 at 16:58

Ciarán

asked Nov 11 at 16:58

Ciarán

asked Nov 11 at 16:58

Ciarán

asked Nov 11 at 16:58

Ciarán

add a comment |

1 Answer
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ARM shifts are done as part of the second operand in other operations. So you would do something like:

OR r0, r4, r3, LSL #4

OR r0, r0, r2, LSL #8

OR r0, r0, r1, LSL #12

though this does not do the 'mask' part if the other bits of your source registers are non-zero.

answered Nov 11 at 17:15

Chris Dodd

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
2
down vote

accepted

ARM shifts are done as part of the second operand in other operations. So you would do something like:

OR r0, r4, r3, LSL #4

OR r0, r0, r2, LSL #8

OR r0, r0, r1, LSL #12

though this does not do the 'mask' part if the other bits of your source registers are non-zero.

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

add a comment |

up vote
2
down vote

accepted

ARM shifts are done as part of the second operand in other operations. So you would do something like:

OR r0, r4, r3, LSL #4

OR r0, r0, r2, LSL #8

OR r0, r0, r1, LSL #12

though this does not do the 'mask' part if the other bits of your source registers are non-zero.

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

add a comment |

up vote
2
down vote

accepted

ARM shifts are done as part of the second operand in other operations. So you would do something like:

OR r0, r4, r3, LSL #4

OR r0, r0, r2, LSL #8

OR r0, r0, r1, LSL #12

though this does not do the 'mask' part if the other bits of your source registers are non-zero.

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

ARM shifts are done as part of the second operand in other operations. So you would do something like:

OR r0, r4, r3, LSL #4

OR r0, r0, r2, LSL #8

OR r0, r0, r1, LSL #12

though this does not do the 'mask' part if the other bits of your source registers are non-zero.

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

answered Nov 11 at 17:15

Chris Dodd

80.1k680159

add a comment |

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