How to find the absolute value of an integer in Two's complement in ARM

up vote
2
down vote

favorite

If I have -2 (11111111111111111111111111111110), is there a neat ARM instruction or a series of such that will make it (00000000000000000000000000000010). OR or XOR would not work from what I have tried since I loose the 30th bit.

Thank you

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

1

ARM's negate instruction is rsb dst, src, #0 (reverse-subtract). You can tst / predicated-rsb. I think that's what C++ compilers will do when inlining / optimizing std::abs, but you should try compiling an abs function with optimization enabled.
– Peter Cordes
Nov 15 at 2:21

which arm instruction set? did you look at NEG? you do need the compare as shown in the checked answer...
– old_timer
Nov 15 at 15:48

add a comment |

up vote
2
down vote

favorite

Thank you

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

1

ARM's negate instruction is rsb dst, src, #0 (reverse-subtract). You can tst / predicated-rsb. I think that's what C++ compilers will do when inlining / optimizing std::abs, but you should try compiling an abs function with optimization enabled.
– Peter Cordes
Nov 15 at 2:21

which arm instruction set? did you look at NEG? you do need the compare as shown in the checked answer...
– old_timer
Nov 15 at 15:48

add a comment |

up vote
2
down vote

favorite

Thank you

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

Thank you

assembly arm twos-complement absolute-value

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

edited Nov 15 at 15:52

Peter Cordes

117k16178305

edited Nov 15 at 15:52

Peter Cordes

117k16178305

edited Nov 15 at 15:52

Peter Cordes

117k16178305

asked Nov 15 at 1:59

mdrjjn

437

asked Nov 15 at 1:59

mdrjjn

437

asked Nov 15 at 1:59

mdrjjn

437

1

ARM's negate instruction is rsb dst, src, #0 (reverse-subtract). You can tst / predicated-rsb. I think that's what C++ compilers will do when inlining / optimizing std::abs, but you should try compiling an abs function with optimization enabled.
– Peter Cordes
Nov 15 at 2:21

which arm instruction set? did you look at NEG? you do need the compare as shown in the checked answer...
– old_timer
Nov 15 at 15:48

add a comment |

1

ARM's negate instruction is rsb dst, src, #0 (reverse-subtract). You can tst / predicated-rsb. I think that's what C++ compilers will do when inlining / optimizing std::abs, but you should try compiling an abs function with optimization enabled.
– Peter Cordes
Nov 15 at 2:21

which arm instruction set? did you look at NEG? you do need the compare as shown in the checked answer...
– old_timer
Nov 15 at 15:48

ARM's negate instruction is rsb dst, src, #0 (reverse-subtract). You can tst / predicated-rsb. I think that's what C++ compilers will do when inlining / optimizing std::abs, but you should try compiling an abs function with optimization enabled.
– Peter Cordes
Nov 15 at 2:21

which arm instruction set? did you look at NEG? you do need the compare as shown in the checked answer...
– old_timer
Nov 15 at 15:48

add a comment |

1 Answer
1

active

oldest

votes

up vote
4
down vote

accepted

For finding the absolute value of an integer, use a comparison and a subtraction.

@ input in r0

cmp r0, #0          @ is r0 < 0?

rsbmi r0, r0 #0     @ if yes, r0 = 0 - r0

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

2

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53311360%2fhow-to-find-the-absolute-value-of-an-integer-in-twos-complement-in-arm%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
4
down vote

accepted

For finding the absolute value of an integer, use a comparison and a subtraction.

@ input in r0

cmp r0, #0          @ is r0 < 0?

rsbmi r0, r0 #0     @ if yes, r0 = 0 - r0

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

2

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

add a comment |

up vote
4
down vote

accepted

For finding the absolute value of an integer, use a comparison and a subtraction.

@ input in r0

cmp r0, #0          @ is r0 < 0?

rsbmi r0, r0 #0     @ if yes, r0 = 0 - r0

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

2

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

add a comment |

up vote
4
down vote

accepted

For finding the absolute value of an integer, use a comparison and a subtraction.

@ input in r0

cmp r0, #0          @ is r0 < 0?

rsbmi r0, r0 #0     @ if yes, r0 = 0 - r0

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

For finding the absolute value of an integer, use a comparison and a subtraction.

@ input in r0

cmp r0, #0          @ is r0 < 0?

rsbmi r0, r0 #0     @ if yes, r0 = 0 - r0

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

edited Nov 15 at 14:09

answered Nov 15 at 7:13

fuz

56.8k14124253

answered Nov 15 at 7:13

fuz

56.8k14124253

answered Nov 15 at 7:13

fuz

56.8k14124253

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

2

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

add a comment |

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

2

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

mvn a bitwise NOT, ones-complement inversion rather than two's complement. infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204j/…. Like I commented, you can use rsbmi r0, #0
– Peter Cordes
Nov 15 at 11:36

@PeterCordes Clearly you are right. I though for a second that mvn stood for “move negated.” That said, did you get my email?
– fuz
Nov 15 at 11:39

I did, thanks for the reminder. I should have some time to look at that today.
– Peter Cordes
Nov 15 at 11:43

@PeterCordes I'm looking forwards to your comments!
– fuz
Nov 15 at 11:44

Worth noting that if you're using an ARMv7 or ARMv8 device, you will be using the Thumb-2 instruction set which does not include conditional execution of non-branch instructions. You will need an it mi before the rsbmi. Many assemblers will insert this for you, though some will warn because you're getting an instruction you didn't explicitly request. See community.arm.com/processors/b/blog/posts/…
– cooperised
Nov 15 at 13:44

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

Some of your past answers have not been well-received, and you're in danger of being blocked from answering.

Please pay close attention to the following guidance:

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Cfrgtkky