Return to lfsr.h CVS log

Up to [PGP] / pgp / src

Annotation of pgp/src/lfsr.h, revision 1.1

1.1     ! root        1: /*     lfsr.h - C header include file for lfsr.c
        !             2: **     Linear Feedback Shift Register (LFSR) routines
        !             3: **     (c) 1988 Philip Zimmermann.  All rights reserved.
        !             4: */
        !             5: 
        !             6: 
        !             7: /* Elaborate protection mechanisms to assure no redefinitions of types...*/
        !             8: #ifndef BYTESTUFF
        !             9: #define BYTESTUFF
        !            10: typedef unsigned char byte;    /* values are 0-255 */
        !            11: typedef byte *byteptr; /* pointer to byte */
        !            12: typedef char *string;  /* pointer to ASCII character string */
        !            13: #endif /* if BYTESTUFF not already defined */
        !            14: 
        !            15: 
        !            16: /*
        !            17: **     steplfsr256 - Step big linear feedback shift register (LFSR)
        !            18: **     256 cycles.  Use primitive polynomial:  X^255 + X^82 + X^0
        !            19: **     Actually runs 8 LFSR's in parallel, outputting a whole byte
        !            20: **     with each step.
        !            21: */
        !            22: void steplfsr256(register byteptr lfsr);
        !            23: 
        !            24: /*
        !            25: **     getlfsr - get 1 byte from lfsr buffer.  Must be macro, not function.
        !            26: **     Calls steplfsr256() if necessary to replenish lfsr buffer.
        !            27: */
        !            28: #define getlfsr(lfsr,rtail) (rtail ? lfsr[--rtail] : \
        !            29:                                (steplfsr256(lfsr),lfsr[--rtail]))
        !            30: 
        !            31: 
        !            32: /*
        !            33: **     initlfsr - initialize linear feedback shift register
        !            34: */
        !            35: void initlfsr(byteptr seed, short size, byteptr lfsr, byte *rtail);
        !            36: 
        !            37: /*
        !            38: **     stomplfsr - inverts about half the bits in an LFSR.
        !            39: **
        !            40: **     If the LFSR has a "rail" of almost all 0's or almost all 1's in
        !            41: **     the same bit position, it will perform poorly as a random number
        !            42: **     generator.  This function will probably fix this condition.
        !            43: */
        !            44: void stomplfsr(byteptr lfsr);
        !            45: 
        !            46: 

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.