20060303a

1 files changed, 54 insertions, 0 deletions

diff --git a/libmp/port/mpright.c b/libmp/port/mpright.c
new file mode 100644
index 00000000..03039177
--- /dev/null
+++ b/libmp/port/mpright.c
@@ -0,0 +1,54 @@
+#include "os.h"
+#include <mp.h>
+#include "dat.h"
+
+// res = b >> shift
+void
+mpright(mpint *b, int shift, mpint *res)
+{
+	int d, l, r, i;
+	mpdigit this, last;
+
+	res->sign = b->sign;
+	if(b->top==0){
+		res->top = 0;
+		return;
+	}
+
+	// a negative right shift is a left shift
+	if(shift < 0){
+		mpleft(b, -shift, res);
+		return;
+	}
+
+	if(res != b)
+		mpbits(res, b->top*Dbits - shift);
+	d = shift/Dbits;
+	r = shift - d*Dbits;
+	l = Dbits - r;
+
+	//  shift all the bits out == zero
+	if(d>=b->top){
+		res->top = 0;
+		return;
+	}
+
+	// special case digit shifts
+	if(r == 0){
+		for(i = 0; i < b->top-d; i++)
+			res->p[i] = b->p[i+d];
+	} else {
+		last = b->p[d];
+		for(i = 0; i < b->top-d-1; i++){
+			this = b->p[i+d+1];
+			res->p[i] = (this<<l) | (last>>r);
+			last = this;
+		}
+		res->p[i++] = last>>r;
+	}
+	while(i > 0 && res->p[i-1] == 0)
+		i--;
+	res->top = i;
+	if(i==0)
+		res->sign = 1;
+}