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when I var_dump these constants,these values isGMP_ROUND_ZERO 0
GMP_ROUND_PLUSINF 1
GMP_ROUND_MINUSINF 2
GMP_VERSION "5.0.2"
Here is a table showing the output from gmp_export given gmp_init( 0x0123456789ABCDEF ) and various inputs parameters on a little endian 64-bit platform.
NOTE that the underscores in the table are used to illustrate the separation between "word"s (which are either char, short, int, or long).
+-----------+-----+--------+-------------------------+
| Word Size | Sig | Endian | gmp_export Hex Result |
+-----------+-----+--------+-------------------------+
| 1 byte | MSW | little | 01_23_45_67_89_AB_CD_EF |
+-----------+-----+--------+-------------------------+
| 1 byte | MSW | big | 01_23_45_67_89_AB_CD_EF |
+-----------+-----+--------+-------------------------+
| 1 byte | LSW | little | EF_CD_AB_89_67_45_23_01 |
+-----------+-----+--------+-------------------------+
| 1 byte | LSW | big | EF_CD_AB_89_67_45_23_01 |
+-----------+-----+--------+-------------------------+
| 2 bytes | MSW | little | 2301_6745_AB89_EFCD |
+-----------+-----+--------+-------------------------+
| 2 bytes | MSW | big | 0123_4567_89AB_CDEF |
+-----------+-----+--------+-------------------------+
| 2 bytes | LSW | little | EFCD_AB89_6745_2301 |
+-----------+-----+--------+-------------------------+
| 2 bytes | LSW | big | CDEF_89AB_4567_0123 |
+-----------+-----+--------+-------------------------+
| 4 bytes | MSW | little | 67452301_EFCDAB89 |
+-----------+-----+--------+-------------------------+
| 4 bytes | MSW | big | 01234567_89ABCDEF |
+-----------+-----+--------+-------------------------+
| 4 bytes | LSW | little | EFCDAB89_67452301 |
+-----------+-----+--------+-------------------------+
| 4 bytes | LSW | big | 89ABCDEF_01234567 |
+-----------+-----+--------+-------------------------+
| 8 bytes | MSW | little | EFCDAB8967452301 |
+-----------+-----+--------+-------------------------+
| 8 bytes | MSW | big | 0123456789ABCDEF |
+-----------+-----+--------+-------------------------+
| 8 bytes | LSW | little | EFCDAB8967452301 |
+-----------+-----+--------+-------------------------+
| 8 bytes | LSW | big | 0123456789ABCDEF |
+-----------+-----+--------+-------------------------+
See the full table at https://pastebin.com/2GX4L3dq
My conclusions and infrences:
* gmp_export appears to strips sign data as if calling gmp_abs( $gmp_resource )
* MSW might stand for Most Signifigant Word (order) as the most significant (highest digit) words come first.
\- A "word" is a numeric type (char, short, int, or long) determined by the $word_size parameter
* LSW might stand for Least Signifigant Word (order) as the least significant (lowest digit) words come first.
* endianness only matters when you are using a word size greater than 1 because, with a word size of 1, each byte is copied over. With a word size of 2, each short is copied over. 4 is int. When copying numbers larger than a byte, endianness does matter because it changes the order of the bytes within the size of the unit. A 2-byte short will have its bytes swapped depending upon the endianness, but the bits in each byte will remain the same.
This note was too long to post, so I had to move the code to make the above table to https://pastebin.com/gWLU4GF8