Remove the vestigial mem4 and mem6 memory allocators. Add the

SQLITE_ZERO_MALLOC compile-time option and the mem0.c module to
handle memory allocation for that case. (CVS 5848)

FossilOrigin-Name: 4651f590f0b8bf13938b2b15d5082136e763af8d

src/mem0.c

@@ -0,0 +1,61 @@
+/*
+** 2008 October 28
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** This file contains a no-op memory allocation drivers for use when
+** SQLITE_ZERO_MALLOC is defined.  The allocation drivers implemented
+** here always fail.  SQLite will not operate with these drivers.  These
+** are merely placeholders.  Real drivers must be substituted using
+** sqlite3_config() before SQLite will operate.
+**
+** $Id: mem0.c,v 1.1 2008/10/28 18:58:20 drh Exp $
+*/
+#include "sqliteInt.h"
+
+/*
+** This version of the memory allocator is the default.  It is
+** used when no other memory allocator is specified using compile-time
+** macros.
+*/
+#ifdef SQLITE_ZERO_MALLOC
+
+/*
+** No-op versions of all memory allocation routines
+*/
+static void *sqlite3MemMalloc(int nByte){ return 0; }
+static void sqlite3MemFree(void *pPrior){ return; }
+static void *sqlite3MemRealloc(void *pPrior, int nByte){ return 0; }
+static int sqlite3MemSize(void *pPrior){ return 0; }
+static int sqlite3MemRoundup(int n){ return n; }
+static int sqlite3MemInit(void *NotUsed){ return SQLITE_OK; }
+static void sqlite3MemShutdown(void *NotUsed){ return; }
+
+/*
+** This routine is the only routine in this file with external linkage.
+**
+** Populate the low-level memory allocation function pointers in
+** sqlite3GlobalConfig.m with pointers to the routines in this file.
+*/
+void sqlite3MemSetDefault(void){
+  static const sqlite3_mem_methods defaultMethods = {
+     sqlite3MemMalloc,
+     sqlite3MemFree,
+     sqlite3MemRealloc,
+     sqlite3MemSize,
+     sqlite3MemRoundup,
+     sqlite3MemInit,
+     sqlite3MemShutdown,
+     0
+  };
+  sqlite3_config(SQLITE_CONFIG_MALLOC, &defaultMethods);
+}
+
+#endif /* SQLITE_ZERO_MALLOC */