Edit - Code Golf Stack Exchange

You are not logged in. Your edit will be placed in a queue until it is peer reviewed.

We welcome edits that make the post easier to understand and more valuable for readers. Because community members review edits, please try to make the post substantially better than how you found it, for example, by fixing grammar or adding additional resources and hyperlinks.

Required fields*

Rev

Required fields*

Am I not good enough for you?

Background:

The current Perfect Numbers challenge is rather flawed and complicated, since it asks you to output in a complex format involving the factors of the number. This is a purely decision-problem repost of the challenge.

Challenge

Given a positive integer through any standard input format, distinguish between whether it is perfect or not.

A perfect number is a number that is equal to the sum of all its proper divisors (its positive divisors less than itself). For example, \6ドル\$ is a perfect number, since its divisors are \1,2,3ドル\$, which sum up to \6ドル\$, while \12ドル\$ is not a perfect number since its divisors ( \1,2,3,4,6ドル\$ ) sum up to \16ドル\$, not \12ドル\$.

Test Cases:

Imperfect:
1,12,13,18,20,1000,33550335
Perfect:
6,28,496,8128,33550336,8589869056

Rules

Your program doesn't have to complete the larger test cases, if there's memory or time constraints, but it should be theoretically able to if it were given more memory/time.
Output can be two distinct and consistent values through any allowed output format. If it isn't immediately obvious what represents Perfect/Imperfect, please make sure to specify in your answer.

Answer*

# Machine Language (x86 32-bit), <s>24</s> 23 bytes

This is a macro that takes an unsigned integer in EAX as input (N), and outputs the result in the Zero Flag (set=perfect, clear=imperfect). It also outputs a result in the Carry Flag (set=abundant, clear=non-abundant). As such, it's actually an answer for both this question and [An abundance of integers!](https://codegolf.stackexchange.com/questions/110708/an-abundance-of-integers), requiring no modification.

It's based on [640KB's abundant numbers answer](https://codegolf.stackexchange.com/questions/110708/an-abundance-of-integers/179016#179016), with the two additional optimizations from [l4m2's answer](https://codegolf.stackexchange.com/questions/110708/an-abundance-of-integers/179303#179303), where the divisors are subtracted from N instead of added to it (thus simultaneously setting the flags for the return value). An input of 1 is correctly handled, costing <s>3</s> 2 bytes.

```
89 C1 89 C3 9E EB 0E 31 D2 50 F7 F1 58 85 D2 75 04 29 CB 72 02 E2 F0
```

[Try it online!](https://tio.run/##jVZNb@M4DD1Hv4KYSxpMOusk7e42RQ/ZbAvsYjGXuRQzKAzZomMNbMmw5DSdP9@lbPlrEkziQxtJ5CP5SJHixmAeZW/XCTf5e6LLnFt4/O8J8IBxZXmUIawYC43lpV2zSYYcAI2cwzdpwgLLBGP70u4Lt49KhKOzXO8BojeL8E1VeYTlx@XLHKYwZSkeQlHlRZhpXTh0LUzkFXg6B56xiUlLWmRzuGETrkRzEByeaCXc6kBQQTBlkzgvGsHpHa2@RwhAXhkbGrkLlYwolNDkPMtaTSe6mV5fkfzHxYydFl63wOkQONe/wE3HuCdl1z7KV12KlhYihR/8PgqKa@Vt13wTuc44kAEhQlPwGE9g1NQGh02wYROp4hqIdQqtVYwJvVFodyLaWbQLR@qNA7BAYH8Gp/0YZa/PpdCKDA2hFqyvh/U7@K/3hIT83j3EungDqYrKegdpYTU8bp/ZWDG6UPGvXtHwNIGfvnsSg5gb/EnXwGJO9WPh69NDAK7wtvSjg/ru@Ii1snXwLRQe4qwSCLqUO6l41qJxAxyE3EujS5bw2PqCb9EOuvQppz99RFSRJTz@/QxXqdylTZ7pitZIgq7ZrAMoKpMO2PAAhu8HvrRanRJt1AkYKzVizuz6cfMMv42oL1ysR3ZKNFaXeGzB0sFxXDIhjZxLJYiaBwjmIK3XNYB7VNlbz7P6cYJnQlDazusDqSqEugK7NFdRWx9xb/VLFdmSqG/zAEmpc1ce92BTSreReZVZrlBXZuDAqY9Sk3K1I29tilBWSkm1A6utaymuVAza5izJ@M64nJ3Bq3HQVqWCPc8q/NQTELtM0ZUayf@TuHKkCnWKpspBJ21cxsVfR4qiixFSbs64QLWLKEhHV@XoLswhR15HSGkionhUKcGVnZ8BdES8IihCJW4In9Sdu3UilX51mz5ml4AzaFRjlB53WTteP7GuMPqrVKN3V4zVzegXoD3l6zMOXP37dQZUrtQPFvTPt7OzSp9J66FpIg8g80vVtrWtbWOrZfy8se2s0XLGlFbXF2tuWntNr/P@CkxkLPESy5tZ66/rZZ4k50KH8T5@GLgRUd/unpRJ28bY6EGh8DWTCq8XL8PxRcPKWDEaXwETGEsar@17YtRX2aRpeBH9OsTprplN9UH/HnAPCWpm7hXSjM/4WLrparyZPz6IoeFu8ko2nOY11GDouTl6yewlWnzXZR1VjrzGiPOgGc5OcRnQ598oPdVDidXq9jZYLZ0QJ6GCGgOGy6HxTsKfrY/Vb0/YaNmmYGqKh@N/GI0fiSAi@HCzvLu5@/2P5d3tB@az7Pbp/fL@Pw "Assembly (fasm, x64, Linux) – Try It Online")

```
89 C1 mov ecx, eax ; copy input number into ECX
89 C3 mov ebx, eax ; copy input number into EBX
9E sahf ; in case input number is 1, let ZF=0 and CF=0
EB 0E jmp cont_loop ; exclude original number as a divisor
 fact_loop: 
31 D2 xor edx, edx ; clear EDX (high word for dividend)
50 push eax ; save original dividend
F7 F1 div ecx ; divide EDX:EAX / ECX
58 pop eax ; restore dividend
85 D2 test edx, edx ; if remainder = 0, it divides evenly
75 04 jnz cont_loop ; if not, continue loop
29 CB sub ebx, ecx ; Subtract divisor from EBX; this simultaneously
 ; changes the running total, and sets the flags for
 ; the return value.
72 02 jc done ; If CF=1, the sum of divisors subtracted from EBX has
 ; exceeded our input number, meaning it is abundant,
 ; and we need to exit the loop now to return this
 ; result in the flags.
 cont_loop: 
E2 F0 loop fact_loop 
 done: ; return value:
 ; (JZ) = ZF=1 = perfect
 ; (JNZ) = ZF=0 = imperfect
 ; (JC) = CF=1 = abundant
 ; (JNC) = CF=0 = non-abundant
 ; (JA) = CF=0 and ZF=0 = deficient
 ; (JNA) = CF=1 or ZF=1 = non-deficient
```

If this is an answer to a challenge…

…Be sure to follow the challenge specification. However, please refrain from exploiting obvious loopholes. Answers abusing any of the standard loopholes are considered invalid. If you think a specification is unclear or underspecified, comment on the question instead.
…Try to optimize your score. For instance, answers to code-golf challenges should attempt to be as short as possible. You can always include a readable version of the code in addition to the competitive one. Explanations of your answer make it more interesting to read and are very much encouraged.
…Include a short header which indicates the language(s) of your code and its score, as defined by the challenge.

More generally…

…Please make sure to answer the question and provide sufficient detail.
…Avoid asking for help, clarification or responding to other answers (use comments instead).

Draft saved

Draft discarded

Edit Summary*

Cancel

\$\begingroup\$ 22 bytes \$\endgroup\$

l4m2
– l4m2

2021年03月10日 22:09:14 +00:00
Commented Mar 10, 2021 at 22:09
\$\begingroup\$ @l4m2 That's a great way to do abundant numbers with full 32-bit input support costing just 2 bytes, but as I know you know, this is perfect numbers :-) \$\endgroup\$

Deadcode
– Deadcode

2021年03月11日 15:14:42 +00:00
Commented Mar 11, 2021 at 15:14
\$\begingroup\$ Hmm didn't go up to check question \$\endgroup\$

l4m2
– l4m2

2021年03月11日 17:01:10 +00:00
Commented Mar 11, 2021 at 17:01
\$\begingroup\$ Is there any case where the difference happens to be times of 2^32? \$\endgroup\$

l4m2
– l4m2

2021年03月11日 17:01:59 +00:00
Commented Mar 11, 2021 at 17:01
\$\begingroup\$ @l4m2 I checked a couple days ago, generating all aliquot sums up to 2^32-1, and there are none where σ(n) = n + k*2^32. Nevertheless, I didn't want to remove my jc instruction even though it'd save 2 bytes, because I really like having a single routine that handles both abundant and perfect numbers, and also would work with any operand size (not just 32 bits)... but yep, you have a point, technically I could drop 2 bytes this way. But that would be like hard-coding the perfect numbers rather than detecting them. \$\endgroup\$

Deadcode
– Deadcode

2021年03月11日 17:17:19 +00:00
Commented Mar 11, 2021 at 17:17

Add a comment |

How to Edit

Correct minor typos or mistakes
Clarify meaning without changing it
Add related resources or links
Always respect the author’s intent
Don’t use edits to reply to the author

How to Format

create code fences with backticks ` or tildes ~
```
like so
```
add language identifier to highlight code
```python
def function(foo):
print(foo)
```
put returns between paragraphs
for linebreak add 2 spaces at end
_italic_ or **bold**
indent code by 4 spaces
backtick escapes `like _so_`
quote by placing > at start of line
to make links (use https whenever possible)

<https://example.com>

[example](https://example.com)

<a href="https://example.com">example</a>
MathJax equations \$\sin^2 \theta\$

formatting help »
answering help »

MathJax help »

How to Tag

A tag is a keyword or label that categorizes your question with other, similar questions. Choose one or more (up to 5) tags that will help answerers to find and interpret your question.

complete the sentence: my question is about...
use tags that describe things or concepts that are essential, not incidental to your question
favor using existing popular tags
read the descriptions that appear below the tag

If your question is primarily about a topic for which you can't find a tag:

combine multiple words into single-words with hyphens (e.g. code-golf), up to a maximum of 35 characters
creating new tags is a privilege; if you can't yet create a tag you need, then post this question without it, then ask the community to create it for you

popular tags »