Move init_primes_array out into its own file.

Mostly because I just had a neat idea about how to expose that large
mutable array without it being a mutable global variable: make it a
static in its own module, and expose only a _pointer_ to it, which is
const-qualified.

While I'm there, changed the name to something more descriptive.

Recipe

@@ -281,6 +281,9 @@ UXSSH    = SSH uxnoise uxagentc uxgss uxshare
 # SFTP implementation (pscp, psftp).
 SFTP     = psftpcommon sftp sftpcommon logging cmdline
 
+# Components of the prime-generation system.
+SSHPRIME = sshprime smallprimes
+
 # Miscellaneous objects appearing in all the utilities, or all the
 # network ones, or the Unix or Windows subsets of those in turn.
 MISC     = misc utils marshal memory stripctrl wcwidth
@@ -294,7 +297,7 @@ UXMISC   = MISCNET UXMISCCOMMON uxproxy uxutils
 
 # SSH server.
 SSHSERVER = SSHCOMMON sshserver settings be_none logging ssh2kex-server
-         + ssh2userauth-server sshrsag sshprime ssh2connection-server
+         + ssh2userauth-server sshrsag SSHPRIME ssh2connection-server
          + sesschan sftpcommon sftpserver proxy cproxy ssh1login-server
          + ssh1connection-server scpserver
 
@@ -347,7 +350,7 @@ pageant  : [G] winpgnt pageant sshrsa sshpubk sshdes ARITH sshmd5 version
 	 + sshauxcrypt sshhmac wincapi winnps winnpc winhsock errsock winnet
 	 + winhandl callback be_misc winselgui winhandl LIBS
 
-puttygen : [G] winpgen KEYGEN sshprime sshdes ARITH sshmd5 version
+puttygen : [G] winpgen KEYGEN SSHPRIME sshdes ARITH sshmd5 version
          + sshrand winnoise sshsha winstore MISC winctrls sshrsa sshdss winmisc
          + sshpubk sshaes sshsh256 sshsh512 IMPORT winutils puttygen.res
          + tree234 notiming winhelp winnojmp CONF LIBS wintime sshecc sshprng
@@ -366,7 +369,7 @@ puttytel : [X] GTKTERM uxmisc misc ldisc settings uxsel U_BE_NOSSH
 plink    : [U] uxplink uxcons NONSSH UXSSH U_BE_ALL logging UXMISC uxsignal
          + ux_x11 noterm uxnogtk sessprep cmdline clicons uxcliloop
 
-PUTTYGEN_UNIX = KEYGEN sshprime sshdes ARITH sshmd5 version sshprng
+PUTTYGEN_UNIX = KEYGEN SSHPRIME sshdes ARITH sshmd5 version sshprng
          + sshrand uxnoise sshsha MISC sshrsa sshdss uxcons uxstore uxmisc
          + sshpubk sshaes sshsh256 sshsh512 IMPORT puttygen.res time tree234
          + uxgen notiming CONF sshecc uxnogtk sshauxcrypt sshhmac
@@ -395,9 +398,9 @@ osxlaunch : [UT] osxlaunch
 
 fuzzterm : [UT] UXTERM CHARSET MISC version uxmisc uxucs fuzzterm time settings
 	 + uxstore be_none uxnogtk memory
-testcrypt : [UT] testcrypt SSHCRYPTO sshprng sshprime sshpubk marshal utils
+testcrypt : [UT] testcrypt SSHCRYPTO sshprng SSHPRIME sshpubk marshal utils
           + memory tree234 uxutils KEYGEN
-testcrypt : [C] testcrypt SSHCRYPTO sshprng sshprime sshpubk marshal utils
+testcrypt : [C] testcrypt SSHCRYPTO sshprng SSHPRIME sshpubk marshal utils
           + memory tree234 winmiscs KEYGEN
 testsc    : [UT] testsc SSHCRYPTO marshal utils memory tree234 wildcard
           + sshmac uxutils sshpubk

smallprimes.c

@@ -0,0 +1,44 @@
+/*
+ * smallprimes.c: implementation of the array of small primes defined
+ * in sshkeygen.h.
+ */
+
+#include <assert.h>
+#include "ssh.h"
+#include "sshkeygen.h"
+
+/* The real array that stores the primes. It has to be writable in
+ * this module, but outside this module, we only expose the
+ * const-qualified pointer 'smallprimes' so that nobody else can
+ * accidentally overwrite it. */
+static unsigned short smallprimes_array[NSMALLPRIMES];
+
+const unsigned short *const smallprimes = smallprimes_array;
+
+void init_smallprimes(void)
+{
+    if (smallprimes_array[0])
+        return;                        /* already done */
+
+    bool A[65536];
+
+    for (size_t i = 2; i < lenof(A); i++)
+        A[i] = true;
+
+    for (size_t i = 2; i < lenof(A); i++) {
+        if (!A[i])
+            continue;
+        for (size_t j = 2*i; j < lenof(A); j += i)
+            A[j] = false;
+    }
+
+    size_t pos = 0;
+    for (size_t i = 2; i < lenof(A); i++) {
+        if (A[i]) {
+            assert(pos < NSMALLPRIMES);
+            smallprimes_array[pos++] = i;
+        }
+    }
+
+    assert(pos == NSMALLPRIMES);
+}

sshkeygen.h

@@ -0,0 +1,12 @@
+/*
+ * sshkeygen.h: routines used internally to key generation.
+ */
+
+/*
+ * A table of all the primes that fit in a 16-bit integer. Call
+ * init_primes_array to make sure it's been initialised.
+ */
+
+#define NSMALLPRIMES 6542 /* number of primes < 65536 */
+extern const unsigned short *const smallprimes;
+void init_smallprimes(void);

sshprime.c

@@ -5,6 +5,7 @@
 #include <assert.h>
 #include "ssh.h"
 #include "mpint.h"
+#include "sshkeygen.h"
 
 /*
  * This prime generation algorithm is pretty much cribbed from
@@ -107,34 +108,6 @@
  * but 1s.)
  */
 
-static unsigned short primes[6542]; /* # primes < 65536 */
-#define NPRIMES (lenof(primes))
-
-static void init_primes_array(void)
-{
-    if (primes[0])
-        return;                        /* already done */
-
-    bool A[65536];
-
-    for (size_t i = 2; i < lenof(A); i++)
-        A[i] = true;
-
-    for (size_t i = 2; i < lenof(A); i++) {
-        if (!A[i])
-            continue;
-        for (size_t j = 2*i; j < lenof(A); j += i)
-            A[j] = false;
-    }
-
-    size_t pos = 0;
-    for (size_t i = 2; i < lenof(A); i++)
-        if (A[i])
-            primes[pos++] = i;
-
-    assert(pos == NPRIMES);
-}
-
 static unsigned short mp_mod_short(mp_int *x, unsigned short modulus)
 {
     /*
@@ -176,7 +149,7 @@ mp_int *primegen(
     int bits, int modulus, int residue, mp_int *factor,
     int phase, progfn_t pfn, void *pfnparam, unsigned firstbits)
 {
-    init_primes_array();
+    init_smallprimes();
 
     int progress = 0;
 
@@ -220,16 +193,16 @@ mp_int *primegen(
      */
 
     /* List the moduli */
-    unsigned long moduli[NPRIMES + 1];
-    for (size_t i = 0; i < NPRIMES; i++)
-        moduli[i] = primes[i];
-    moduli[NPRIMES] = modulus;
+    unsigned long moduli[NSMALLPRIMES + 1];
+    for (size_t i = 0; i < NSMALLPRIMES; i++)
+        moduli[i] = smallprimes[i];
+    moduli[NSMALLPRIMES] = modulus;
 
     /* Find the residue of our starting number mod each of them. Also
      * set up the multipliers array which tells us how each one will
      * change when we increment the number (which isn't just 1 if
      * we're incrementing by multiples of factor). */
-    unsigned long residues[NPRIMES + 1], multipliers[NPRIMES + 1];
+    unsigned long residues[NSMALLPRIMES + 1], multipliers[NSMALLPRIMES + 1];
     for (size_t i = 0; i < lenof(moduli); i++) {
         residues[i] = mp_mod_short(p, moduli[i]);
         if (factor)
@@ -239,7 +212,8 @@ mp_int *primegen(
     }
 
     /* Adjust the last entry so that it avoids a residue other than zero */
-    residues[NPRIMES] = (residues[NPRIMES] + modulus - residue) % modulus;
+    residues[NSMALLPRIMES] = (residues[NSMALLPRIMES] + modulus
+                              - residue) % modulus;
 
     /*
      * Now loop until no residue in that list is zero, to find a