also patch fp_mul() as proposed by tom on the ML [1]

[1] https://groups.google.com/forum/#!topic/libtom/MdbS1vcLhCU

src/mul/fp_mul.c

@@ -12,16 +12,23 @@
 /* c = a * b */
 void fp_mul(fp_int *A, fp_int *B, fp_int *C)
 {
-    int   y, yy;
+    int   y, old_used;
+#if FP_SIZE >= 48
+    int   yy;
+#endif
+
+    old_used = C->used;
 
     /* call generic if we're out of range */
     if (A->used + B->used > FP_SIZE) {
        fp_mul_comba(A, B, C);
-       return ;
+       goto clean;
     }
 
      y  = MAX(A->used, B->used);
+#if FP_SIZE >= 48
      yy = MIN(A->used, B->used);
+#endif
     /* pick a comba (unrolled 4/8/16/32 x or rolled) based on the size
        of the largest input.  We also want to avoid doing excess mults if the
        inputs are not close to the next power of two.  That is, for example,
@@ -31,95 +38,99 @@ void fp_mul(fp_int *A, fp_int *B, fp_int *C)
 #if defined(TFM_MUL3) && FP_SIZE >= 6
         if (y <= 3) {
            fp_mul_comba3(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL4) && FP_SIZE >= 8
         if (y == 4) {
            fp_mul_comba4(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL6) && FP_SIZE >= 12
         if (y <= 6) {
            fp_mul_comba6(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL7) && FP_SIZE >= 14
         if (y == 7) {
            fp_mul_comba7(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL8) && FP_SIZE >= 16
         if (y == 8) {
            fp_mul_comba8(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL9) && FP_SIZE >= 18
         if (y == 9) {
            fp_mul_comba9(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL12) && FP_SIZE >= 24
         if (y <= 12) {
            fp_mul_comba12(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL17) && FP_SIZE >= 34
         if (y <= 17) {
            fp_mul_comba17(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 
 #if defined(TFM_SMALL_SET) && FP_SIZE >= 32
         if (y <= 16) {
            fp_mul_comba_small(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL20) && FP_SIZE >= 40
         if (y <= 20) {
            fp_mul_comba20(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL24) && FP_SIZE >= 48
         if (yy >= 16 && y <= 24) {
            fp_mul_comba24(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL28) && FP_SIZE >= 56
         if (yy >= 20 && y <= 28) {
            fp_mul_comba28(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL32) && FP_SIZE >= 64
         if (yy >= 24 && y <= 32) {
            fp_mul_comba32(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL48) && FP_SIZE >= 96
         if (yy >= 40 && y <= 48) {
            fp_mul_comba48(A,B,C);
-           return;
+           goto clean;
         }
 #endif
 #if defined(TFM_MUL64) && FP_SIZE >= 128
         if (yy >= 56 && y <= 64) {
            fp_mul_comba64(A,B,C);
-           return;
+           goto clean;
         }
 #endif
         fp_mul_comba(A,B,C);
+clean:
+    for (y = C->used; y < old_used; y++) {
+       C->dp[y] = 0;
+    }
 }