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-rw-r--r--security/nss/lib/util/secport.c732
1 files changed, 732 insertions, 0 deletions
diff --git a/security/nss/lib/util/secport.c b/security/nss/lib/util/secport.c
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index 000000000..0eea0cda0
--- /dev/null
+++ b/security/nss/lib/util/secport.c
@@ -0,0 +1,732 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * secport.c - portability interfaces for security libraries
+ *
+ * This file abstracts out libc functionality that libsec depends on
+ *
+ * NOTE - These are not public interfaces
+ */
+
+#include "seccomon.h"
+#include "prmem.h"
+#include "prerror.h"
+#include "plarena.h"
+#include "secerr.h"
+#include "prmon.h"
+#include "nssilock.h"
+#include "secport.h"
+#include "prenv.h"
+#include "prinit.h"
+
+#ifdef DEBUG
+#define THREADMARK
+#endif /* DEBUG */
+
+#ifdef THREADMARK
+#include "prthread.h"
+#endif /* THREADMARK */
+
+#if defined(XP_UNIX) || defined(XP_OS2) || defined(XP_BEOS)
+#include <stdlib.h>
+#else
+#include "wtypes.h"
+#endif
+
+#define SET_ERROR_CODE /* place holder for code to set PR error code. */
+
+#ifdef THREADMARK
+typedef struct threadmark_mark_str {
+ struct threadmark_mark_str *next;
+ void *mark;
+} threadmark_mark;
+
+#endif /* THREADMARK */
+
+/* The value of this magic must change each time PORTArenaPool changes. */
+#define ARENAPOOL_MAGIC 0xB8AC9BDF
+
+#define CHEAP_ARENAPOOL_MAGIC 0x3F16BB09
+
+typedef struct PORTArenaPool_str {
+ PLArenaPool arena;
+ PRUint32 magic;
+ PRLock *lock;
+#ifdef THREADMARK
+ PRThread *marking_thread;
+ threadmark_mark *first_mark;
+#endif
+} PORTArenaPool;
+
+/* locations for registering Unicode conversion functions.
+ * XXX is this the appropriate location? or should they be
+ * moved to client/server specific locations?
+ */
+PORTCharConversionFunc ucs4Utf8ConvertFunc;
+PORTCharConversionFunc ucs2Utf8ConvertFunc;
+PORTCharConversionWSwapFunc ucs2AsciiConvertFunc;
+
+/* NSPR memory allocation functions (PR_Malloc, PR_Calloc, and PR_Realloc)
+ * use the PRUint32 type for the size parameter. Before we pass a size_t or
+ * unsigned long size to these functions, we need to ensure it is <= half of
+ * the maximum PRUint32 value to avoid truncation and catch a negative size.
+ */
+#define MAX_SIZE (PR_UINT32_MAX >> 1)
+
+void *
+PORT_Alloc(size_t bytes)
+{
+ void *rv = NULL;
+
+ if (bytes <= MAX_SIZE) {
+ /* Always allocate a non-zero amount of bytes */
+ rv = PR_Malloc(bytes ? bytes : 1);
+ }
+ if (!rv) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ }
+ return rv;
+}
+
+void *
+PORT_Realloc(void *oldptr, size_t bytes)
+{
+ void *rv = NULL;
+
+ if (bytes <= MAX_SIZE) {
+ rv = PR_Realloc(oldptr, bytes);
+ }
+ if (!rv) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ }
+ return rv;
+}
+
+void *
+PORT_ZAlloc(size_t bytes)
+{
+ void *rv = NULL;
+
+ if (bytes <= MAX_SIZE) {
+ /* Always allocate a non-zero amount of bytes */
+ rv = PR_Calloc(1, bytes ? bytes : 1);
+ }
+ if (!rv) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ }
+ return rv;
+}
+
+void
+PORT_Free(void *ptr)
+{
+ if (ptr) {
+ PR_Free(ptr);
+ }
+}
+
+void
+PORT_ZFree(void *ptr, size_t len)
+{
+ if (ptr) {
+ memset(ptr, 0, len);
+ PR_Free(ptr);
+ }
+}
+
+char *
+PORT_Strdup(const char *str)
+{
+ size_t len = PORT_Strlen(str) + 1;
+ char *newstr;
+
+ newstr = (char *)PORT_Alloc(len);
+ if (newstr) {
+ PORT_Memcpy(newstr, str, len);
+ }
+ return newstr;
+}
+
+void
+PORT_SetError(int value)
+{
+#ifdef DEBUG_jp96085
+ PORT_Assert(value != SEC_ERROR_REUSED_ISSUER_AND_SERIAL);
+#endif
+ PR_SetError(value, 0);
+ return;
+}
+
+int
+PORT_GetError(void)
+{
+ return (PR_GetError());
+}
+
+/********************* Arena code follows *****************************
+ * ArenaPools are like heaps. The memory in them consists of large blocks,
+ * called arenas, which are allocated from the/a system heap. Inside an
+ * ArenaPool, the arenas are organized as if they were in a stack. Newly
+ * allocated arenas are "pushed" on that stack. When you attempt to
+ * allocate memory from an ArenaPool, the code first looks to see if there
+ * is enough unused space in the top arena on the stack to satisfy your
+ * request, and if so, your request is satisfied from that arena.
+ * Otherwise, a new arena is allocated (or taken from NSPR's list of freed
+ * arenas) and pushed on to the stack. The new arena is always big enough
+ * to satisfy the request, and is also at least a minimum size that is
+ * established at the time that the ArenaPool is created.
+ *
+ * The ArenaMark function returns the address of a marker in the arena at
+ * the top of the arena stack. It is the address of the place in the arena
+ * on the top of the arena stack from which the next block of memory will
+ * be allocated. Each ArenaPool has its own separate stack, and hence
+ * marks are only relevant to the ArenaPool from which they are gotten.
+ * Marks may be nested. That is, a thread can get a mark, and then get
+ * another mark.
+ *
+ * It is intended that all the marks in an ArenaPool may only be owned by a
+ * single thread. In DEBUG builds, this is enforced. In non-DEBUG builds,
+ * it is not. In DEBUG builds, when a thread gets a mark from an
+ * ArenaPool, no other thread may acquire a mark in that ArenaPool while
+ * that mark exists, that is, until that mark is unmarked or released.
+ * Therefore, it is important that every mark be unmarked or released when
+ * the creating thread has no further need for exclusive ownership of the
+ * right to manage the ArenaPool.
+ *
+ * The ArenaUnmark function discards the ArenaMark at the address given,
+ * and all marks nested inside that mark (that is, acquired from that same
+ * ArenaPool while that mark existed). It is an error for a thread other
+ * than the mark's creator to try to unmark it. When a thread has unmarked
+ * all its marks from an ArenaPool, then another thread is able to set
+ * marks in that ArenaPool. ArenaUnmark does not deallocate (or "pop") any
+ * memory allocated from the ArenaPool since the mark was created.
+ *
+ * ArenaRelease "pops" the stack back to the mark, deallocating all the
+ * memory allocated from the arenas in the ArenaPool since that mark was
+ * created, and removing any arenas from the ArenaPool that have no
+ * remaining active allocations when that is done. It implicitly releases
+ * any marks nested inside the mark being explicitly released. It is the
+ * only operation, other than destroying the arenapool, that potentially
+ * reduces the number of arenas on the stack. Otherwise, the stack grows
+ * until the arenapool is destroyed, at which point all the arenas are
+ * freed or returned to a "free arena list", depending on their sizes.
+ */
+PLArenaPool *
+PORT_NewArena(unsigned long chunksize)
+{
+ PORTArenaPool *pool;
+
+ if (chunksize > MAX_SIZE) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ return NULL;
+ }
+ pool = PORT_ZNew(PORTArenaPool);
+ if (!pool) {
+ return NULL;
+ }
+ pool->magic = ARENAPOOL_MAGIC;
+ pool->lock = PZ_NewLock(nssILockArena);
+ if (!pool->lock) {
+ PORT_Free(pool);
+ return NULL;
+ }
+ PL_InitArenaPool(&pool->arena, "security", chunksize, sizeof(double));
+ return (&pool->arena);
+}
+
+void
+PORT_InitCheapArena(PORTCheapArenaPool *pool, unsigned long chunksize)
+{
+ pool->magic = CHEAP_ARENAPOOL_MAGIC;
+ PL_InitArenaPool(&pool->arena, "security", chunksize, sizeof(double));
+}
+
+void *
+PORT_ArenaAlloc(PLArenaPool *arena, size_t size)
+{
+ void *p = NULL;
+
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+
+ if (size <= 0) {
+ size = 1;
+ }
+
+ if (size > MAX_SIZE) {
+ /* you lose. */
+ } else
+ /* Is it one of ours? Assume so and check the magic */
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ PZ_Lock(pool->lock);
+#ifdef THREADMARK
+ /* Most likely one of ours. Is there a thread id? */
+ if (pool->marking_thread &&
+ pool->marking_thread != PR_GetCurrentThread()) {
+ /* Another thread holds a mark in this arena */
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return NULL;
+ } /* tid != null */
+#endif /* THREADMARK */
+ PL_ARENA_ALLOCATE(p, arena, size);
+ PZ_Unlock(pool->lock);
+ } else {
+ PL_ARENA_ALLOCATE(p, arena, size);
+ }
+
+ if (!p) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ }
+
+ return (p);
+}
+
+void *
+PORT_ArenaZAlloc(PLArenaPool *arena, size_t size)
+{
+ void *p;
+
+ if (size <= 0)
+ size = 1;
+
+ p = PORT_ArenaAlloc(arena, size);
+
+ if (p) {
+ PORT_Memset(p, 0, size);
+ }
+
+ return (p);
+}
+
+static PRCallOnceType setupUseFreeListOnce;
+static PRBool useFreeList;
+
+static PRStatus
+SetupUseFreeList(void)
+{
+ useFreeList = (PR_GetEnvSecure("NSS_DISABLE_ARENA_FREE_LIST") == NULL);
+ return PR_SUCCESS;
+}
+
+/*
+ * If zero is true, zeroize the arena memory before freeing it.
+ */
+void
+PORT_FreeArena(PLArenaPool *arena, PRBool zero)
+{
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+ PRLock *lock = (PRLock *)0;
+ size_t len = sizeof *arena;
+
+ if (!pool)
+ return;
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ len = sizeof *pool;
+ lock = pool->lock;
+ PZ_Lock(lock);
+ }
+ if (zero) {
+ PL_ClearArenaPool(arena, 0);
+ }
+ (void)PR_CallOnce(&setupUseFreeListOnce, &SetupUseFreeList);
+ if (useFreeList) {
+ PL_FreeArenaPool(arena);
+ } else {
+ PL_FinishArenaPool(arena);
+ }
+ PORT_ZFree(arena, len);
+ if (lock) {
+ PZ_Unlock(lock);
+ PZ_DestroyLock(lock);
+ }
+}
+
+void
+PORT_DestroyCheapArena(PORTCheapArenaPool *pool)
+{
+ (void)PR_CallOnce(&setupUseFreeListOnce, &SetupUseFreeList);
+ if (useFreeList) {
+ PL_FreeArenaPool(&pool->arena);
+ } else {
+ PL_FinishArenaPool(&pool->arena);
+ }
+}
+
+void *
+PORT_ArenaGrow(PLArenaPool *arena, void *ptr, size_t oldsize, size_t newsize)
+{
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+ PORT_Assert(newsize >= oldsize);
+
+ if (newsize > MAX_SIZE) {
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ return NULL;
+ }
+
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ PZ_Lock(pool->lock);
+ /* Do we do a THREADMARK check here? */
+ PL_ARENA_GROW(ptr, arena, oldsize, (newsize - oldsize));
+ PZ_Unlock(pool->lock);
+ } else {
+ PL_ARENA_GROW(ptr, arena, oldsize, (newsize - oldsize));
+ }
+
+ return (ptr);
+}
+
+void *
+PORT_ArenaMark(PLArenaPool *arena)
+{
+ void *result;
+
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ PZ_Lock(pool->lock);
+#ifdef THREADMARK
+ {
+ threadmark_mark *tm, **pw;
+ PRThread *currentThread = PR_GetCurrentThread();
+
+ if (!pool->marking_thread) {
+ /* First mark */
+ pool->marking_thread = currentThread;
+ } else if (currentThread != pool->marking_thread) {
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return NULL;
+ }
+
+ result = PL_ARENA_MARK(arena);
+ PL_ARENA_ALLOCATE(tm, arena, sizeof(threadmark_mark));
+ if (!tm) {
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ return NULL;
+ }
+
+ tm->mark = result;
+ tm->next = (threadmark_mark *)NULL;
+
+ pw = &pool->first_mark;
+ while (*pw) {
+ pw = &(*pw)->next;
+ }
+
+ *pw = tm;
+ }
+#else /* THREADMARK */
+ result = PL_ARENA_MARK(arena);
+#endif /* THREADMARK */
+ PZ_Unlock(pool->lock);
+ } else {
+ /* a "pure" NSPR arena */
+ result = PL_ARENA_MARK(arena);
+ }
+ return result;
+}
+
+/*
+ * This function accesses the internals of PLArena, which is why it needs
+ * to use the NSPR internal macro PL_MAKE_MEM_UNDEFINED before the memset
+ * calls.
+ *
+ * We should move this function to NSPR as PL_ClearArenaAfterMark or add
+ * a PL_ARENA_CLEAR_AND_RELEASE macro.
+ *
+ * TODO: remove the #ifdef PL_MAKE_MEM_UNDEFINED tests when NSPR 4.10+ is
+ * widely available.
+ */
+static void
+port_ArenaZeroAfterMark(PLArenaPool *arena, void *mark)
+{
+ PLArena *a = arena->current;
+ if (a->base <= (PRUword)mark && (PRUword)mark <= a->avail) {
+/* fast path: mark falls in the current arena */
+#ifdef PL_MAKE_MEM_UNDEFINED
+ PL_MAKE_MEM_UNDEFINED(mark, a->avail - (PRUword)mark);
+#endif
+ memset(mark, 0, a->avail - (PRUword)mark);
+ } else {
+ /* slow path: need to find the arena that mark falls in */
+ for (a = arena->first.next; a; a = a->next) {
+ PR_ASSERT(a->base <= a->avail && a->avail <= a->limit);
+ if (a->base <= (PRUword)mark && (PRUword)mark <= a->avail) {
+#ifdef PL_MAKE_MEM_UNDEFINED
+ PL_MAKE_MEM_UNDEFINED(mark, a->avail - (PRUword)mark);
+#endif
+ memset(mark, 0, a->avail - (PRUword)mark);
+ a = a->next;
+ break;
+ }
+ }
+ for (; a; a = a->next) {
+ PR_ASSERT(a->base <= a->avail && a->avail <= a->limit);
+#ifdef PL_MAKE_MEM_UNDEFINED
+ PL_MAKE_MEM_UNDEFINED((void *)a->base, a->avail - a->base);
+#endif
+ memset((void *)a->base, 0, a->avail - a->base);
+ }
+ }
+}
+
+static void
+port_ArenaRelease(PLArenaPool *arena, void *mark, PRBool zero)
+{
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ PZ_Lock(pool->lock);
+#ifdef THREADMARK
+ {
+ threadmark_mark **pw;
+
+ if (PR_GetCurrentThread() != pool->marking_thread) {
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return /* no error indication available */;
+ }
+
+ pw = &pool->first_mark;
+ while (*pw && (mark != (*pw)->mark)) {
+ pw = &(*pw)->next;
+ }
+
+ if (!*pw) {
+ /* bad mark */
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return /* no error indication available */;
+ }
+
+ *pw = (threadmark_mark *)NULL;
+
+ if (zero) {
+ port_ArenaZeroAfterMark(arena, mark);
+ }
+ PL_ARENA_RELEASE(arena, mark);
+
+ if (!pool->first_mark) {
+ pool->marking_thread = (PRThread *)NULL;
+ }
+ }
+#else /* THREADMARK */
+ if (zero) {
+ port_ArenaZeroAfterMark(arena, mark);
+ }
+ PL_ARENA_RELEASE(arena, mark);
+#endif /* THREADMARK */
+ PZ_Unlock(pool->lock);
+ } else {
+ if (zero) {
+ port_ArenaZeroAfterMark(arena, mark);
+ }
+ PL_ARENA_RELEASE(arena, mark);
+ }
+}
+
+void
+PORT_ArenaRelease(PLArenaPool *arena, void *mark)
+{
+ port_ArenaRelease(arena, mark, PR_FALSE);
+}
+
+/*
+ * Zeroize the arena memory before releasing it.
+ */
+void
+PORT_ArenaZRelease(PLArenaPool *arena, void *mark)
+{
+ port_ArenaRelease(arena, mark, PR_TRUE);
+}
+
+void
+PORT_ArenaUnmark(PLArenaPool *arena, void *mark)
+{
+#ifdef THREADMARK
+ PORTArenaPool *pool = (PORTArenaPool *)arena;
+ if (ARENAPOOL_MAGIC == pool->magic) {
+ threadmark_mark **pw;
+
+ PZ_Lock(pool->lock);
+
+ if (PR_GetCurrentThread() != pool->marking_thread) {
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return /* no error indication available */;
+ }
+
+ pw = &pool->first_mark;
+ while (((threadmark_mark *)NULL != *pw) && (mark != (*pw)->mark)) {
+ pw = &(*pw)->next;
+ }
+
+ if ((threadmark_mark *)NULL == *pw) {
+ /* bad mark */
+ PZ_Unlock(pool->lock);
+ PORT_SetError(SEC_ERROR_NO_MEMORY);
+ PORT_Assert(0);
+ return /* no error indication available */;
+ }
+
+ *pw = (threadmark_mark *)NULL;
+
+ if (!pool->first_mark) {
+ pool->marking_thread = (PRThread *)NULL;
+ }
+
+ PZ_Unlock(pool->lock);
+ }
+#endif /* THREADMARK */
+}
+
+char *
+PORT_ArenaStrdup(PLArenaPool *arena, const char *str)
+{
+ int len = PORT_Strlen(str) + 1;
+ char *newstr;
+
+ newstr = (char *)PORT_ArenaAlloc(arena, len);
+ if (newstr) {
+ PORT_Memcpy(newstr, str, len);
+ }
+ return newstr;
+}
+
+/********************** end of arena functions ***********************/
+
+/****************** unicode conversion functions ***********************/
+/*
+ * NOTE: These conversion functions all assume that the multibyte
+ * characters are going to be in NETWORK BYTE ORDER, not host byte
+ * order. This is because the only time we deal with UCS-2 and UCS-4
+ * are when the data was received from or is going to be sent out
+ * over the wire (in, e.g. certificates).
+ */
+
+void
+PORT_SetUCS4_UTF8ConversionFunction(PORTCharConversionFunc convFunc)
+{
+ ucs4Utf8ConvertFunc = convFunc;
+}
+
+void
+PORT_SetUCS2_ASCIIConversionFunction(PORTCharConversionWSwapFunc convFunc)
+{
+ ucs2AsciiConvertFunc = convFunc;
+}
+
+void
+PORT_SetUCS2_UTF8ConversionFunction(PORTCharConversionFunc convFunc)
+{
+ ucs2Utf8ConvertFunc = convFunc;
+}
+
+PRBool
+PORT_UCS4_UTF8Conversion(PRBool toUnicode, unsigned char *inBuf,
+ unsigned int inBufLen, unsigned char *outBuf,
+ unsigned int maxOutBufLen, unsigned int *outBufLen)
+{
+ if (!ucs4Utf8ConvertFunc) {
+ return sec_port_ucs4_utf8_conversion_function(toUnicode,
+ inBuf, inBufLen, outBuf, maxOutBufLen, outBufLen);
+ }
+
+ return (*ucs4Utf8ConvertFunc)(toUnicode, inBuf, inBufLen, outBuf,
+ maxOutBufLen, outBufLen);
+}
+
+PRBool
+PORT_UCS2_UTF8Conversion(PRBool toUnicode, unsigned char *inBuf,
+ unsigned int inBufLen, unsigned char *outBuf,
+ unsigned int maxOutBufLen, unsigned int *outBufLen)
+{
+ if (!ucs2Utf8ConvertFunc) {
+ return sec_port_ucs2_utf8_conversion_function(toUnicode,
+ inBuf, inBufLen, outBuf, maxOutBufLen, outBufLen);
+ }
+
+ return (*ucs2Utf8ConvertFunc)(toUnicode, inBuf, inBufLen, outBuf,
+ maxOutBufLen, outBufLen);
+}
+
+PRBool
+PORT_ISO88591_UTF8Conversion(const unsigned char *inBuf,
+ unsigned int inBufLen, unsigned char *outBuf,
+ unsigned int maxOutBufLen, unsigned int *outBufLen)
+{
+ return sec_port_iso88591_utf8_conversion_function(inBuf, inBufLen,
+ outBuf, maxOutBufLen, outBufLen);
+}
+
+PRBool
+PORT_UCS2_ASCIIConversion(PRBool toUnicode, unsigned char *inBuf,
+ unsigned int inBufLen, unsigned char *outBuf,
+ unsigned int maxOutBufLen, unsigned int *outBufLen,
+ PRBool swapBytes)
+{
+ if (!ucs2AsciiConvertFunc) {
+ return PR_FALSE;
+ }
+
+ return (*ucs2AsciiConvertFunc)(toUnicode, inBuf, inBufLen, outBuf,
+ maxOutBufLen, outBufLen, swapBytes);
+}
+
+/* Portable putenv. Creates/replaces an environment variable of the form
+ * envVarName=envValue
+ */
+int
+NSS_PutEnv(const char *envVarName, const char *envValue)
+{
+ SECStatus result = SECSuccess;
+ char *encoded;
+ int putEnvFailed;
+#ifdef _WIN32
+ PRBool setOK;
+
+ setOK = SetEnvironmentVariable(envVarName, envValue);
+ if (!setOK) {
+ SET_ERROR_CODE
+ return SECFailure;
+ }
+#endif
+
+ encoded = (char *)PORT_ZAlloc(strlen(envVarName) + 2 + strlen(envValue));
+ strcpy(encoded, envVarName);
+ strcat(encoded, "=");
+ strcat(encoded, envValue);
+
+ putEnvFailed = putenv(encoded); /* adopt. */
+ if (putEnvFailed) {
+ SET_ERROR_CODE
+ result = SECFailure;
+ PORT_Free(encoded);
+ }
+ return result;
+}
+
+/*
+ * Perform a constant-time compare of two memory regions. The return value is
+ * 0 if the memory regions are equal and non-zero otherwise.
+ */
+int
+NSS_SecureMemcmp(const void *ia, const void *ib, size_t n)
+{
+ const unsigned char *a = (const unsigned char *)ia;
+ const unsigned char *b = (const unsigned char *)ib;
+ size_t i;
+ unsigned char r = 0;
+
+ for (i = 0; i < n; ++i) {
+ r |= *a++ ^ *b++;
+ }
+
+ return r;
+}