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According to Intel's definition of a x86 16-bit Word, a Quad Word refers a 64-bit word.
Contents
long long or long
Microsoft 64-bit C-compiler long is still 32-bit Double Word, while 64-bit GCC uses 64-bit Quad Words as longs. Other compiler require "long long" for 64-bit types.
typedef unsigned long QWORD;
typedef unsigned long long QWORD;Bitboards
Quad words are used as bitboard datatype:
typedef QWORD U64;
typedef QWORD Bitboard;Ranges
language |
type |
min |
max |
|---|---|---|---|
unsigned long long |
0 |
18,446,744,073,709,551,615 |
|
hexadecimal |
0x0000000000000000 |
0xFFFFFFFFFFFFFFFF |
|
long long |
-9,223,372,036,854,775,808 |
9,223,372,036,854,775,807 |
|
hexadecimal |
0x8000000000000000 |
0x7FFFFFFFFFFFFFFF |
Alignment
Quad Words stored in memory should be stored at byte addresses divisible by eight. Otherwise at runtime it will cause a miss-alignment exception on some processors, or a huge penalty on others.
Endianness
Main article: Endianness.
Litte-endian Layout
The little-endian memory layout, as typical for Intel cpus. For instance the quad word integer 0x0102030405060708
| Address | Byte | Significance |
|---|---|---|
| 0x0000 | 0x08 | LS Byte |
| 0x0001 | 0x07 | |
| 0x0002 | 0x06 | |
| 0x0003 | 0x05 | |
| 0x0004 | 0x04 | |
| 0x0005 | 0x03 | |
| 0x0006 | 0x02 | |
| 0x0008 | 0x01 | MS Byte |
Big-endian Layout
The big-endian memory layout, as typical for Motorola cpus. For instance the quad word integer 0x0102030405060708
| Address | Byte | Significance |
|---|---|---|
| 0x0000 | 0x01 | MS Byte |
| 0x0001 | 0x02 | |
| 0x0002 | 0x03 | |
| 0x0003 | 0x04 | |
| 0x0004 | 0x05 | |
| 0x0005 | 0x06 | |
| 0x0006 | 0x07 | |
| 0x0007 | 0x08 | LS Byte |