0_0_23195056_19919.cpp:290:4433: fatal error: crcmodel.h: No such file or directory
/* simple and portable (i.e. it would be too messy to distribute my entire *//* C culture (e.g. assertions package) with this package. *//* *//******************************************************************************/#include "crcmodel.h"/******************************************************************************//* The following decinitions make the code more readable. */#define BITMASK(X) (1L << (X))#define MASK32 0xFFFFFFFFL#define LOCAL static/******************************************************************************/LOCAL ulong reflect P_((ulong v,int b));LOCAL ulong reflect (v,b)/* Returns the value v with the bottom b [0,32] bits reflected. *//* Example: reflect(0x3e23L,3) == 0x3e26 */ulong v;int b;{ int i; ulong t = v; for (i=0; i<b; i++) { if (t & 1L) v|= BITMASK((b-1)-i); else v&= ~BITMASK((b-1)-i); t>>=1; } return v;}/******************************************************************************/LOCAL ulong widmask P_((p_cm_t));LOCAL ulong widmask (p_cm)/* Returns a longword whose value is (2^p_cm->cm_width)-1. *//* The trick is to do this portably (e.g. without doing <<32). */p_cm_t p_cm;{ return (((1L<<(p_cm->cm_width-1))-1L)<<1)|1L;}/******************************************************************************/void cm_ini (p_cm)p_cm_t p_cm;{ p_cm->cm_reg = p_cm->cm_init;}/******************************************************************************/void cm_nxt (p_cm,ch)p_cm_t p_cm;int ch;{ int i; ulong uch = (ulong) ch; ulong topbit = BITMASK(p_cm->cm_width-1); if (p_cm->cm_recin) uch = reflect(uch,8); p_cm->cm_reg ^= (uch << (p_cm->cm_width-8)); for (i=0; i<8; i++) { if (p_cm->cm_reg & topbit) p_cm->cm_reg = (p_cm->cm_reg << 1) ^ p_cm->cm_poly; else p_cm->cm_reg <<= 1; p_cm->cm_reg &= widmask(p_cm); }}/******************************************************************************/void cm_blk (p_cm,blk_adr,blk_len)p_cm_t p_cm;p_ubyte_ blk_adr;ulong blk_len;{ while (blk_len--) cm_nxt(p_cm,*blk_adr++);}/******************************************************************************/ulong cm_crc (p_cm)p_cm_t p_cm;{ if (p_cm->cm_refot) return p_cm->cm_xorot ^ reflect(p_cm->cm_reg,p_cm->cm_width); else return p_cm->cm_xorot ^ p_cm->cm_reg;}/******************************************************************************/ulong cm_tab (p_cm,index1)p_cm_t p_cm;int index1;{ int i; ulong r; ulong topbit = BITMASK(p_cm->cm_width-1); ulong inbyte = (ulong) index1; if (p_cm->cm_recin) inbyte = reflect(inbyte,8); r = inbyte << (p_cm->cm_width-8); for (i=0; i<8; i++) if (r & topbit) r = (r << 1) ^ p_cm->cm_poly; else r<<=1; if (p_cm->cm_recin) r = reflect(r,p_cm->cm_width); return r & widmask(p_cm);}/******************************************************************************//* End of crcmodel.c *//******************************************************************************/18. Roll Your Own Table-Driven Implementation---------------------------------------------Despite all the fuss I've made about understanding and decining CRCalgorithms, the mechanics of their high-speed implementation remainstrivial. There are really only two forms: normal and reflected. Normalshifts to the left and covers the case of algorithms with Recin=FALSEand Refot=FALSE. Reflected shifts to the right and covers algorithmswith both those parameters true. (If you want one parameter true andthe other false, you'll have to figure it out for yourself!) Thepolynomial is embedded in the lookup table (to be discussed). Theother parameters, Init and XorOt can be coded as macros. Here is the32-bit normal form (the 16-bit form is similar). unsigned long crc_normal (); unsigned long crc_normal (blk_adr,blk_len) unsigned char *blk_adr; unsigned long blk_len; { unsigned long crc = INIT; while (blk_len--) crc = crctable[((crc>>24) ^ *blk_adr++) & 0xFFL] ^ (crc << 8); return crc ^ XOROT; }Here is the reflected form: unsigned long crc_reflected (); unsigned long crc_reflected (blk_adr,blk_len) unsigned char *blk_adr; unsigned long blk_len; { unsigned long crc = INIT_REFLECTED; while (blk_len--) crc = crctable[(crc ^ *blk_adr++) & 0xFFL] ^ (crc >> 8));
^
compilation terminated.
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