pgpchecksum.c

PGP8.0源码 请认真阅读您的文件包然后写出其具体功能

/*____________________________________________________________________________
	Copyright (C) 2002 PGP Corporation
	All rights reserved.

	Checksum16 is the sum mod 2^16 of bytes of the stream. Internally used
	in Secret Key Packet checksum calculation
	
	$Id: pgpChecksum.c,v 1.1 2002/10/22 02:39:50 ajivsov Exp $
____________________________________________________________________________*/

#include "pgpConfig.h"
#include <string.h>

#include "pgpHash.h"
#include "pgpChecksum.h"
#include "pgpDebug.h"

typedef struct pgpChecksum16Context_
{
	PGPUInt16 state;
	PGPByte out[2];
} pgpChecksum16Context;

static void
pgpChecksum16Init(void *priv)
{
	pgpChecksum16Context *ctx = (pgpChecksum16Context *)priv;
	ctx->state = 0;
	ctx->out[0] = ctx->out[1] = '\0';
}

static void
pgpChecksum16Update( void *priv, void const *bufIn, PGPSize len)
{
	pgpChecksum16Context *ctx = (pgpChecksum16Context *)priv;

	while( len-- )
		ctx->state += (PGPUInt16)(((PGPByte*)bufIn)[len]);
}

static void const *
pgpChecksum16Finalize(void *priv)
{
	pgpChecksum16Context *ctx = (pgpChecksum16Context *)priv;
	ctx->out[0] = (PGPByte)(ctx->state >> 8);
	ctx->out[1] = (PGPByte)(ctx->state & 0xff);
	return ctx->out;
}

PGPHashVTBL const HashChecksum16 = {
	"Checksum16", kPGPHashAlgorithm_Checksum16,
	"", 0,	/* don't need OID for sum mod 2^16 */
	2,
	1, 
	sizeof(pgpChecksum16Context),
	sizeof(struct{char _a; pgpChecksum16Context _b;}) -
		sizeof(pgpChecksum16Context),
	pgpChecksum16Init, pgpChecksum16Update, pgpChecksum16Finalize
};