119 lines
4.3 KiB
Markdown
119 lines
4.3 KiB
Markdown
---
|
|
title: Endianness
|
|
TARGET DECK: Obsidian::STEM
|
|
FILE TAGS: binary::endian
|
|
tags:
|
|
- binary
|
|
- endian
|
|
---
|
|
|
|
## Overview
|
|
|
|
Platforms with multi-byte objects must establish the object's address and byte ordering. Objects are typically addressed by the smallest address of the bytes used. Bytes are ordered either in **big-endian** or **little-endian**. In big-endian, the most significant byte is listed first. In little-endian, the least significant byte is ordered first.
|
|
|
|
%%ANKI
|
|
Basic
|
|
Platforms with multi-byte objects must establish what two conventions?
|
|
Back: The object's address and byte ordering.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283766-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How are multi-byte objects typically addressed?
|
|
Back: By the smallest address of the bytes used.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283768-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How are bytes of multi-byte objects typically ordered?
|
|
Back: As big-endian or little-endian.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283770-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What is endianness?
|
|
Back: The ordering of bytes of a multi-byte object.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283771-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does it mean for a byte to be "most significant"?
|
|
Back: It contribute most to the byte's (decimal) value.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283773-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does it mean for a byte to be "least significant"?
|
|
Back: It contribute least to the byte's (decimal) value.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283774-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does it mean to be big-endian?
|
|
Back: The most significant byte is ordered first.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283776-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
What does it mean to be little-endian?
|
|
Back: The least significant byte is ordered first.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283777-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How are bytes of `int32_t x = 0x01234567` written in big-endian?
|
|
Back: `0x01 0x23 0x45 0x67`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
Tags: c17
|
|
<!--ID: 1707661283779-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Basic
|
|
How are bytes of `int32_t x = 0x01234567` written in little-endian?
|
|
Back: `0x67 0x45 0x23 0x01`
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
Tags: c17
|
|
<!--ID: 1707661283780-->
|
|
END%%
|
|
|
|
%%ANKI
|
|
Cloze
|
|
Many microprocessors chips are {bi-endian} meaning they can be {configured as either big- or little-endian}.
|
|
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
|
|
<!--ID: 1707661283782-->
|
|
END%%
|
|
|
|
```c
|
|
#include <stdint.h>
|
|
#include <stdio.h>
|
|
|
|
int main() {
|
|
int32_t x = 0x01234567;
|
|
for (int i = 0; i < 4; ++i) {
|
|
printf("%.2x ", ((unsigned char *)(&x))[i]);
|
|
}
|
|
}
|
|
```
|
|
|
|
The above snippet can be used to check endianness on the current machine. If big-endian, the output should be `01 23 45 67`. If little-endian, `67 45 23 01`.
|
|
|
|
## References
|
|
|
|
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016. |