dropbear: tomsfastmath/src/addsub/s_fp

Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a with Makefile.in renamed

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-:33fd2f3499d2
+:a362b62d38b2
+/* TomsFastMath, a fast ISO C bignum library.
+*
+* This project is meant to fill in where LibTomMath
+* falls short.  That is speed ;-)
+*
+* This project is public domain and free for all purposes.
+*
+* Tom St Denis, [email protected]
+*/
+#include <tfm.h>
+/* unsigned subtraction ||a|| >= ||b|| ALWAYS! */
+void s_fp_sub(fp_int *a, fp_int *b, fp_int *c)
+{
+int      x, oldbused, oldused;
+fp_word  t;
+oldused  = c->used;
+oldbused = b->used;
+c->used  = a->used;
+t       = 0;
+for (x = 0; x < oldbused; x++) {
+t         = ((fp_word)a->dp[x]) - (((fp_word)b->dp[x]) + t);
+c->dp[x]  = (fp_digit)t;
+t         = (t >> DIGIT_BIT)&1;
+}
+for (; x < a->used; x++) {
+t         = ((fp_word)a->dp[x]) - t;
+c->dp[x]  = (fp_digit)t;
+t         = (t >> DIGIT_BIT)&1;
+}
+for (; x < oldused; x++) {
+c->dp[x] = 0;
+}
+fp_clamp(c);
+}
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */

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