dropbear: bn_mp_cnt_lsb.c comparison

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+:22d5cf7d4b1a
+/* 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://math.libtomcrypt.org
+*/
+#include <tommath.h>
+static const int lnz[16] = {
+4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
+};
+/* Counts the number of lsbs which are zero before the first zero bit */
+int mp_cnt_lsb(mp_int *a)
+{
+int x;
+mp_digit q, qq;
+/* easy out */
+if (mp_iszero(a) == 1) {
+return 0;
+}
+/* scan lower digits until non-zero */
+for (x = 0; x < a->used && a->dp[x] == 0; x++);
+q = a->dp[x];
+x *= DIGIT_BIT;
+/* now scan this digit until a 1 is found */
+if ((q & 1) == 0) {
+do {
+qq  = q & 15;
+x  += lnz[qq];
+q >>= 4;
+} while (qq == 0);
+}
+return x;
+}

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