Salsa20 Implementation: Sum of 2 Words with Carries Suppressed
Clash Royale CLAN TAG#URR8PPP
$begingroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited Feb 27 at 6:46
DannyNiu
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
$endgroup$
add a comment |
$begingroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited Feb 27 at 6:46
DannyNiu
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
$endgroup$
1
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43
add a comment |
$begingroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
edited Feb 27 at 6:46
DannyNiu
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
$endgroup$
I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries suppressed, but what does "carries suppressed" mean. Then I come across some summation notation:
$u=sum_i2^iu_i$
What does the variable "i" mean in this context exactly? I understand summation notation and the index variable, but the context of the spec doesn't elaborate enough for me to know what "i" indexes.
I realize this all may be very rudimentary, but I am a programmer first.
modular-arithmetic xor salsa20
modular-arithmetic xor salsa20
edited Feb 27 at 6:46
DannyNiu
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
edited Feb 27 at 6:46
DannyNiu
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
edited Feb 27 at 6:46
DannyNiu
1,3331629
edited Feb 27 at 6:46
DannyNiu
1,3331629
edited Feb 27 at 6:46
DannyNiu
1,3331629
1,3331629
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
asked Feb 27 at 4:55
whole_lotta_coinswhole_lotta_coins
232
232
1
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43
add a comment |
1
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43
1
1
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered Feb 27 at 5:03
forestforest
4,51911641
$endgroup$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
);
);
, "mathjax-editing");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "281"
;
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',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
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
,
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcrypto.stackexchange.com%2fquestions%2f67635%2fsalsa20-implementation-sum-of-2-words-with-carries-suppressed%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered Feb 27 at 5:03
forestforest
4,51911641
$endgroup$
add a comment |
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered Feb 27 at 5:03
forestforest
4,51911641
$endgroup$
add a comment |
$begingroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered Feb 27 at 5:03
forestforest
4,51911641
$endgroup$
The sum of two words with carries suppressed is just a convoluted way of saying XOR. You don't need to implement any kind of complicated summation operation. Just perform a bitwise-exclusive OR.
See also https://en.wikipedia.org/wiki/Exclusive_or#Computer_science
answered Feb 27 at 5:03
forestforest
4,51911641
edited Feb 27 at 8:19
answered Feb 27 at 5:03
forestforest
4,51911641
answered Feb 27 at 5:03
forestforest
4,51911641
answered Feb 27 at 5:03
forestforest
4,51911641
4,51911641
add a comment |
add a comment |
Thanks for contributing an answer to Cryptography Stack Exchange!
- 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.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcrypto.stackexchange.com%2fquestions%2f67635%2fsalsa20-implementation-sum-of-2-words-with-carries-suppressed%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
1
$begingroup$
$$bigoplus$$
$endgroup$
– kelalaka
Feb 27 at 16:43