--- a/libtommath/bn_s_mp_exptmod.c	Thu Mar 21 23:28:59 2019 +0800
+++ b/libtommath/bn_s_mp_exptmod.c	Fri Jun 26 21:07:34 2020 +0800
@@ -1,252 +1,198 @@
-#include <tommath_private.h>
+#include "tommath_private.h"
 #ifdef BN_S_MP_EXPTMOD_C
-/* LibTomMath, multiple-precision integer library -- Tom St Denis
- *
- * LibTomMath is a library that provides multiple-precision
- * integer arithmetic as well as number theoretic functionality.
- *
- * The library was designed directly after the MPI library by
- * Michael Fromberger but has been written from scratch with
- * additional optimizations in place.
- *
- * The library is free for all purposes without any express
- * guarantee it works.
- *
- * Tom St Denis, [email protected], http://libtom.org
- */
-#ifdef MP_LOW_MEM
-   #define TAB_SIZE 32
-#else
-   #define TAB_SIZE 256
-#endif
-
-int s_mp_exptmod (mp_int * G, mp_int * X, mp_int * P, mp_int * Y, int redmode)
-{
-  mp_int  M[TAB_SIZE], res, mu;
-  mp_digit buf;
-  int     err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
-  int (*redux)(mp_int*,mp_int*,mp_int*);
-
-  /* find window size */
-  x = mp_count_bits (X);
-  if (x <= 7) {
-    winsize = 2;
-  } else if (x <= 36) {
-    winsize = 3;
-  } else if (x <= 140) {
-    winsize = 4;
-  } else if (x <= 450) {
-    winsize = 5;
-  } else if (x <= 1303) {
-    winsize = 6;
-  } else if (x <= 3529) {
-    winsize = 7;
-  } else {
-    winsize = 8;
-  }
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
 
 #ifdef MP_LOW_MEM
-    if (winsize > 5) {
-       winsize = 5;
-    }
+#   define TAB_SIZE 32
+#   define MAX_WINSIZE 5
+#else
+#   define TAB_SIZE 256
+#   define MAX_WINSIZE 0
 #endif
 
-  /* init M array */
-  /* init first cell */
-  if ((err = mp_init(&M[1])) != MP_OKAY) {
-     return err; 
-  }
-
-  /* now init the second half of the array */
-  for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
-    if ((err = mp_init(&M[x])) != MP_OKAY) {
-      for (y = 1<<(winsize-1); y < x; y++) {
-        mp_clear (&M[y]);
-      }
-      mp_clear(&M[1]);
-      return err;
-    }
-  }
+mp_err s_mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y, int redmode)
+{
+   mp_int  M[TAB_SIZE], res, mu;
+   mp_digit buf;
+   mp_err   err;
+   int      bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
+   mp_err(*redux)(mp_int *x, const mp_int *m, const mp_int *mu);
 
-  /* create mu, used for Barrett reduction */
-  if ((err = mp_init (&mu)) != MP_OKAY) {
-    goto LBL_M;
-  }
-  
-  if (redmode == 0) {
-     if ((err = mp_reduce_setup (&mu, P)) != MP_OKAY) {
-        goto LBL_MU;
-     }
-     redux = mp_reduce;
-  } else {
-     if ((err = mp_reduce_2k_setup_l (P, &mu)) != MP_OKAY) {
-        goto LBL_MU;
-     }
-     redux = mp_reduce_2k_l;
-  }    
+   /* find window size */
+   x = mp_count_bits(X);
+   if (x <= 7) {
+      winsize = 2;
+   } else if (x <= 36) {
+      winsize = 3;
+   } else if (x <= 140) {
+      winsize = 4;
+   } else if (x <= 450) {
+      winsize = 5;
+   } else if (x <= 1303) {
+      winsize = 6;
+   } else if (x <= 3529) {
+      winsize = 7;
+   } else {
+      winsize = 8;
+   }
+
+   winsize = MAX_WINSIZE ? MP_MIN(MAX_WINSIZE, winsize) : winsize;
 
-  /* create M table
-   *
-   * The M table contains powers of the base, 
-   * e.g. M[x] = G**x mod P
-   *
-   * The first half of the table is not 
-   * computed though accept for M[0] and M[1]
-   */
-  if ((err = mp_mod (G, P, &M[1])) != MP_OKAY) {
-    goto LBL_MU;
-  }
+   /* init M array */
+   /* init first cell */
+   if ((err = mp_init(&M[1])) != MP_OKAY) {
+      return err;
+   }
 
-  /* compute the value at M[1<<(winsize-1)] by squaring 
-   * M[1] (winsize-1) times 
-   */
-  if ((err = mp_copy (&M[1], &M[1 << (winsize - 1)])) != MP_OKAY) {
-    goto LBL_MU;
-  }
+   /* now init the second half of the array */
+   for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
+      if ((err = mp_init(&M[x])) != MP_OKAY) {
+         for (y = 1<<(winsize-1); y < x; y++) {
+            mp_clear(&M[y]);
+         }
+         mp_clear(&M[1]);
+         return err;
+      }
+   }
 
-  for (x = 0; x < (winsize - 1); x++) {
-    /* square it */
-    if ((err = mp_sqr (&M[1 << (winsize - 1)], 
-                       &M[1 << (winsize - 1)])) != MP_OKAY) {
-      goto LBL_MU;
-    }
-
-    /* reduce modulo P */
-    if ((err = redux (&M[1 << (winsize - 1)], P, &mu)) != MP_OKAY) {
-      goto LBL_MU;
-    }
-  }
+   /* create mu, used for Barrett reduction */
+   if ((err = mp_init(&mu)) != MP_OKAY)                           goto LBL_M;
 
-  /* create upper table, that is M[x] = M[x-1] * M[1] (mod P)
-   * for x = (2**(winsize - 1) + 1) to (2**winsize - 1)
-   */
-  for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
-    if ((err = mp_mul (&M[x - 1], &M[1], &M[x])) != MP_OKAY) {
-      goto LBL_MU;
-    }
-    if ((err = redux (&M[x], P, &mu)) != MP_OKAY) {
-      goto LBL_MU;
-    }
-  }
-
-  /* setup result */
-  if ((err = mp_init (&res)) != MP_OKAY) {
-    goto LBL_MU;
-  }
-  mp_set (&res, 1);
+   if (redmode == 0) {
+      if ((err = mp_reduce_setup(&mu, P)) != MP_OKAY)             goto LBL_MU;
+      redux = mp_reduce;
+   } else {
+      if ((err = mp_reduce_2k_setup_l(P, &mu)) != MP_OKAY)        goto LBL_MU;
+      redux = mp_reduce_2k_l;
+   }
 
-  /* set initial mode and bit cnt */
-  mode   = 0;
-  bitcnt = 1;
-  buf    = 0;
-  digidx = X->used - 1;
-  bitcpy = 0;
-  bitbuf = 0;
+   /* create M table
+    *
+    * The M table contains powers of the base,
+    * e.g. M[x] = G**x mod P
+    *
+    * The first half of the table is not
+    * computed though accept for M[0] and M[1]
+    */
+   if ((err = mp_mod(G, P, &M[1])) != MP_OKAY)                    goto LBL_MU;
 
-  for (;;) {
-    /* grab next digit as required */
-    if (--bitcnt == 0) {
-      /* if digidx == -1 we are out of digits */
-      if (digidx == -1) {
-        break;
-      }
-      /* read next digit and reset the bitcnt */
-      buf    = X->dp[digidx--];
-      bitcnt = (int) DIGIT_BIT;
-    }
+   /* compute the value at M[1<<(winsize-1)] by squaring
+    * M[1] (winsize-1) times
+    */
+   if ((err = mp_copy(&M[1], &M[(size_t)1 << (winsize - 1)])) != MP_OKAY) goto LBL_MU;
+
+   for (x = 0; x < (winsize - 1); x++) {
+      /* square it */
+      if ((err = mp_sqr(&M[(size_t)1 << (winsize - 1)],
+                        &M[(size_t)1 << (winsize - 1)])) != MP_OKAY) goto LBL_MU;
 
-    /* grab the next msb from the exponent */
-    y     = (buf >> (mp_digit)(DIGIT_BIT - 1)) & 1;
-    buf <<= (mp_digit)1;
+      /* reduce modulo P */
+      if ((err = redux(&M[(size_t)1 << (winsize - 1)], P, &mu)) != MP_OKAY) goto LBL_MU;
+   }
 
-    /* if the bit is zero and mode == 0 then we ignore it
-     * These represent the leading zero bits before the first 1 bit
-     * in the exponent.  Technically this opt is not required but it
-     * does lower the # of trivial squaring/reductions used
-     */
-    if ((mode == 0) && (y == 0)) {
-      continue;
-    }
+   /* create upper table, that is M[x] = M[x-1] * M[1] (mod P)
+    * for x = (2**(winsize - 1) + 1) to (2**winsize - 1)
+    */
+   for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
+      if ((err = mp_mul(&M[x - 1], &M[1], &M[x])) != MP_OKAY)     goto LBL_MU;
+      if ((err = redux(&M[x], P, &mu)) != MP_OKAY)                goto LBL_MU;
+   }
+
+   /* setup result */
+   if ((err = mp_init(&res)) != MP_OKAY)                          goto LBL_MU;
+   mp_set(&res, 1uL);
 
-    /* if the bit is zero and mode == 1 then we square */
-    if ((mode == 1) && (y == 0)) {
-      if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
-        goto LBL_RES;
-      }
-      if ((err = redux (&res, P, &mu)) != MP_OKAY) {
-        goto LBL_RES;
-      }
-      continue;
-    }
+   /* set initial mode and bit cnt */
+   mode   = 0;
+   bitcnt = 1;
+   buf    = 0;
+   digidx = X->used - 1;
+   bitcpy = 0;
+   bitbuf = 0;
 
-    /* else we add it to the window */
-    bitbuf |= (y << (winsize - ++bitcpy));
-    mode    = 2;
-
-    if (bitcpy == winsize) {
-      /* ok window is filled so square as required and multiply  */
-      /* square first */
-      for (x = 0; x < winsize; x++) {
-        if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
-          goto LBL_RES;
-        }
-        if ((err = redux (&res, P, &mu)) != MP_OKAY) {
-          goto LBL_RES;
-        }
+   for (;;) {
+      /* grab next digit as required */
+      if (--bitcnt == 0) {
+         /* if digidx == -1 we are out of digits */
+         if (digidx == -1) {
+            break;
+         }
+         /* read next digit and reset the bitcnt */
+         buf    = X->dp[digidx--];
+         bitcnt = (int)MP_DIGIT_BIT;
       }
 
-      /* then multiply */
-      if ((err = mp_mul (&res, &M[bitbuf], &res)) != MP_OKAY) {
-        goto LBL_RES;
-      }
-      if ((err = redux (&res, P, &mu)) != MP_OKAY) {
-        goto LBL_RES;
+      /* grab the next msb from the exponent */
+      y     = (buf >> (mp_digit)(MP_DIGIT_BIT - 1)) & 1uL;
+      buf <<= (mp_digit)1;
+
+      /* if the bit is zero and mode == 0 then we ignore it
+       * These represent the leading zero bits before the first 1 bit
+       * in the exponent.  Technically this opt is not required but it
+       * does lower the # of trivial squaring/reductions used
+       */
+      if ((mode == 0) && (y == 0)) {
+         continue;
       }
 
-      /* empty window and reset */
-      bitcpy = 0;
-      bitbuf = 0;
-      mode   = 1;
-    }
-  }
-
-  /* if bits remain then square/multiply */
-  if ((mode == 2) && (bitcpy > 0)) {
-    /* square then multiply if the bit is set */
-    for (x = 0; x < bitcpy; x++) {
-      if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
-        goto LBL_RES;
-      }
-      if ((err = redux (&res, P, &mu)) != MP_OKAY) {
-        goto LBL_RES;
+      /* if the bit is zero and mode == 1 then we square */
+      if ((mode == 1) && (y == 0)) {
+         if ((err = mp_sqr(&res, &res)) != MP_OKAY)               goto LBL_RES;
+         if ((err = redux(&res, P, &mu)) != MP_OKAY)              goto LBL_RES;
+         continue;
       }
 
-      bitbuf <<= 1;
-      if ((bitbuf & (1 << winsize)) != 0) {
-        /* then multiply */
-        if ((err = mp_mul (&res, &M[1], &res)) != MP_OKAY) {
-          goto LBL_RES;
-        }
-        if ((err = redux (&res, P, &mu)) != MP_OKAY) {
-          goto LBL_RES;
-        }
+      /* else we add it to the window */
+      bitbuf |= (y << (winsize - ++bitcpy));
+      mode    = 2;
+
+      if (bitcpy == winsize) {
+         /* ok window is filled so square as required and multiply  */
+         /* square first */
+         for (x = 0; x < winsize; x++) {
+            if ((err = mp_sqr(&res, &res)) != MP_OKAY)            goto LBL_RES;
+            if ((err = redux(&res, P, &mu)) != MP_OKAY)           goto LBL_RES;
+         }
+
+         /* then multiply */
+         if ((err = mp_mul(&res, &M[bitbuf], &res)) != MP_OKAY)  goto LBL_RES;
+         if ((err = redux(&res, P, &mu)) != MP_OKAY)             goto LBL_RES;
+
+         /* empty window and reset */
+         bitcpy = 0;
+         bitbuf = 0;
+         mode   = 1;
       }
-    }
-  }
+   }
+
+   /* if bits remain then square/multiply */
+   if ((mode == 2) && (bitcpy > 0)) {
+      /* square then multiply if the bit is set */
+      for (x = 0; x < bitcpy; x++) {
+         if ((err = mp_sqr(&res, &res)) != MP_OKAY)               goto LBL_RES;
+         if ((err = redux(&res, P, &mu)) != MP_OKAY)              goto LBL_RES;
 
-  mp_exch (&res, Y);
-  err = MP_OKAY;
-LBL_RES:mp_clear (&res);
-LBL_MU:mp_clear (&mu);
+         bitbuf <<= 1;
+         if ((bitbuf & (1 << winsize)) != 0) {
+            /* then multiply */
+            if ((err = mp_mul(&res, &M[1], &res)) != MP_OKAY)     goto LBL_RES;
+            if ((err = redux(&res, P, &mu)) != MP_OKAY)           goto LBL_RES;
+         }
+      }
+   }
+
+   mp_exch(&res, Y);
+   err = MP_OKAY;
+LBL_RES:
+   mp_clear(&res);
+LBL_MU:
+   mp_clear(&mu);
 LBL_M:
-  mp_clear(&M[1]);
-  for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
-    mp_clear (&M[x]);
-  }
-  return err;
+   mp_clear(&M[1]);
+   for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
+      mp_clear(&M[x]);
+   }
+   return err;
 }
 #endif
-
-/* ref:         $Format:%D$ */
-/* git commit:  $Format:%H$ */
-/* commit time: $Format:%ai$ */