Index: class.c
==================================================================
--- class.c
+++ class.c
@@ -645,10 +645,11 @@
   if(!inpstack) fatal("Allocation failed\n");
   inpstack->classfp=classfp;
   inpstack->linenum=linenum;
   inpstack->next=nxt;
   linenum=1;
+  if(main_options['S']) fatal("Cannot use {include} with level hash calculation mode\n");
   if(*name=='.' || *name=='_' || *name=='-' || !*name || name[strspn(name,"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_-abcdefghijklmnopqrstuvwxyz.")])
    ParseError("Improper name of include file \"%s\"\n",name);
   if(main_options['z']) {
     if(strlen(name)<9 || memcmp(name-strlen(name),".include",8)) ParseError("Include file name doesn't end with .include\n");
     classfp=composite_slice(name,0)?:fopen(name,"r");

Index: commandline.doc
==================================================================
--- commandline.doc
+++ commandline.doc
@@ -22,10 +22,15 @@
   Write details of macro expansion to stdout.
 
 -O
   Write a solution Hamster archive with private solutions to stdout.
 
+-S
+  Compute level hashes. The level hashes depend on the class definitions
+  and on the level itself, except for the title. It does not depend on any
+  other files, including other levels, nor the level number.
+
 -T
   Mode for testing some internal functions of Free Hero Mesh and SDL. You
   probably do not need to use this mode yourself.
 
 -U

Index: config.doc
==================================================================
--- config.doc
+++ config.doc
@@ -76,10 +76,15 @@
 
 .gamma
   Gamma setting. If this is set, colours are gamma corrected by the number
   specified here. The default setting is 1.0.
 
+.hash
+  Hash algorithm to use for some features; this must be one of the numbers
+  for hash algorithms listed in the hash.h source file. Can be decimal, or
+  hexadecimal if it starts with "0x".
+
 .imageSize
   The picture size to use, up to 255. If the puzzle set contains pictures
   of the requested size, it will use those, otherwise it will try to make
   the pictures it does have larger by integer scaling; if that also does
   not work, then it is an error.

Index: edit.c
==================================================================
--- edit.c
+++ edit.c
@@ -14,10 +14,11 @@
 #include "sqlite3.h"
 #include "smallxrm.h"
 #include "heromesh.h"
 #include "quarks.h"
 #include "cursorshapes.h"
+#include "hash.h"
 
 EditorRect editrect;
 
 typedef struct {
   Uint16 class;
@@ -850,24 +851,16 @@
     case TY_LEVELSTRING: fprintf(fp," %%%u",(int)v.u); break;
     default: fprintf(fp," ???"); break;
   }
 }
 
-static void export_level(const char*cmd) {
+static void export_level_stream(FILE*fp) {
   Uint32*p=playfield;
   int i;
   Uint32 n;
   Object*o;
-  FILE*fp;
-  if(!cmd || !*cmd) return;
-  fp=popen(cmd,"w");
-  if(!fp) {
-    screen_message("Cannot open pipe");
-    return;
-  }
-  fprintf(fp,"; Free Hero Mesh exported level ID=%d ORD=%d\n",level_id,level_ord);
-  fprint_esc(fp,'@',level_title);
+  if(!main_options['S']) fprint_esc(fp,'@',level_title);
   fprintf(fp,"C %d\nD %d %d\n",level_code,pfwidth,pfheight);
   again:
   for(i=0;i<64*64;i++) {
     n=p[i];
     while(n!=VOIDLINK) {
@@ -888,10 +881,22 @@
     }
   } else {
     fprintf(fp,"W\n");
   }
   for(i=0;i<nlevelstrings;i++) fprint_esc(fp,'%',levelstrings[i]);
+}
+
+static void export_level(const char*cmd) {
+  FILE*fp;
+  if(!cmd || !*cmd) return;
+  fp=popen(cmd,"w");
+  if(!fp) {
+    screen_message("Cannot open pipe");
+    return;
+  }
+  fprintf(fp,"; Free Hero Mesh exported level ID=%d ORD=%d\n",level_id,level_ord);
+  export_level_stream(fp);
   pclose(fp);
 }
 
 static char*import_numbers(char*p,int*x,int*y) {
   if(!p) return 0;
@@ -2042,5 +2047,57 @@
       save_level();
       if(!feof(stdin)) new_level();
     }
   }
 }
+
+static inline void hexout(const unsigned char*p,int n) {
+  while(n--) printf("%02x",*p++);
+}
+
+void make_level_hashes(void) {
+  char*v;
+  FILE*in;
+  FILE*out;
+  unsigned char h1[128];
+  unsigned char h2[128];
+  long long alg;
+  int hn,c,n;
+  optionquery[1]=Q_hash;
+  alg=strtol(xrm_get_resource(resourcedb,optionquery,optionquery,2)?:"",0,0)?:HASH_SHA3_256;
+  hn=hash_length(alg);
+  if(hn<1 || hn>128) fatal("Hash algorithm not valid or too long: %llu (length %d)\n",alg,hn);
+  // Class hash
+  if(main_options['z']) {
+    in=composite_slice(".class",1);
+  } else {
+    v=sqlite3_mprintf("%s.class",basefilename);
+    if(!v) fatal("Allocation failed\n");
+    in=fopen(v,"r");
+    sqlite3_free(v);
+  }
+  if(!in) fatal("Cannot open class file\n");
+  out=hash_stream(alg,0,h1);
+  if(!out) fatal("Allocation failed\n");
+  while((c=fgetc(in))!=EOF) {
+    if(c=='\t') c=' ';
+    if(c!='\r') fputc(c,out);
+  }
+  fclose(in);
+  fclose(out);
+  printf("-1 0 %llx ",alg);
+  hexout(h1,hn);
+  putchar('\n');
+  for(n=0;n<level_nindex;n++) {
+    if(load_level(level_index[n])) fatal("Level load error\n");
+    out=hash_stream(alg,0,h2);
+    if(!out) fatal("Allocation failed\n");
+    fprintf(out,"\x01%llx %x\n",alg,hn);
+    fwrite(h1,1,hn,out);
+    export_level_stream(out);
+    fclose(out);
+    printf("%d 0 %llx ",level_id,alg);
+    hexout(h2,hn);
+    putchar('\n');
+  }
+  exit(0);
+}

Index: heromesh.h
==================================================================
--- heromesh.h
+++ heromesh.h
@@ -363,10 +363,11 @@
 extern EditorRect editrect;
 
 void run_editor(void);
 void write_empty_level_set(FILE*);
 void batch_import(void);
+void make_level_hashes(void);
 
 // == picedit ==
 
 void run_picture_editor(void);
 

Index: main.c
==================================================================
--- main.c
+++ main.c
@@ -1113,11 +1113,11 @@
   if(main_options['n'] && main_options['i']) fatal("Switches -n and -i are conflicting\n");
   if(main_options['n'] || main_options['i']) {
     if(main_options['r']) fatal("Switches -r and -%c are conflicting\n",main_options['i']?'i':'n');
     main_options['x']=1;
   }
-  if(main_options['a'] || main_options['O']) main_options['r']=main_options['x']=1;
+  if(main_options['a'] || main_options['O'] || main_options['S']) main_options['r']=main_options['x']=1;
   if(main_options['p']) main_options['r']=1;
   if(main_options['f']) main_options['x']=1;
   if(!main_options['c']) {
     set_path(argv[0]);
     load_options();
@@ -1169,10 +1169,11 @@
   }
   optionquery[1]=Q_maxTrigger;
   max_trigger=strtol(xrm_get_resource(resourcedb,optionquery,optionquery,2)?:"",0,10);
   if(main_options['a']) run_auto_test();
   if(main_options['O']) export_private_solutions();
+  if(main_options['S']) make_level_hashes();
   if(main_options['x']) {
     if(main_options['i']) {
       batch_import();
       if(main_options['f']) flush_usercache();
       return 0;

Index: man6/heromesh.6
==================================================================
--- man6/heromesh.6
+++ man6/heromesh.6
@@ -21,10 +21,13 @@
 Dump the hash table.
 .IP -L
 Display all tokens being read from the class definition file.
 .IP -O
 Output a solution Hamster archive with private solutions to stdout and then terminate.
+.IP -S
+Compute level hashes.
+Level hashes depend only on the class definition and on the level being hashed, except the title.
 .IP -U
 Enable experimental/unstable features.
 .IP -a
 Autotest levels, ensuring that the provided solution is valid.
 .IP -c