Tables for
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G, ch. 5.6, p. 552

Section CCP4-style compression

P. J. Ellisa and H. J. Bernsteinb*

aStanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025, USA, and bDepartment of Mathematics and Computer Science, Kramer Science Center, Dowling College, Idle Hour Blvd, Oakdale, NY 11769, USA
Correspondence e-mail: CCP4-style compression

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The CCP4-style compression writes the errors in blocks. Each block begins with a 6-bit code. The number of errors in the block is 2n, where n is the value in bits 0 to 2. Bits 3 to 5 encode the number of bits in each error. The data structure is summarized in Table[link].

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Structure of compressed data using the CCP4-style scheme

Value in bits 3 to 5Number of bits in each error
0 0
1 4
2 5
3 6
4 7
5 8
6 16
7 65

1 to 8 Number of elements (64-bit little-endian number)
9 to 16 Minimum element (currently unused)
17 to 24 Maximum element (currently unused)
25 to 32 (Reserved for future use)
33 … Coded data

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