Modular inverse computation.

src/signed/base.rs

@@ -18,6 +18,10 @@ macro_rules! signed_impls {
             pub fn abs(&self) -> $sname {
                 $sname{ negative: false, value: self.value.clone() }
             }
+
+            pub fn is_negative(&self) -> bool {
+                self.negative
+            }
         }
  
         impl From<$sname> for $name {

src/signed/invoc.rs

@@ -1,7 +1,7 @@
 signed_impls!(I192, U192);
 conversion_impls!(I192, U192, I256, U256);
 egcd_impls!(I256, U192, I192);
-modinv_impls!(I192);
+modinv_impls!(U192, I256, U256);
 add_impls!(I256, I320, U320);
 signed_impls!(I256, U256);
 cmp_impls!(I256);
@@ -9,7 +9,7 @@ shift_impls!(I256, U256);
 subtraction_impls!(I256, I320, U320);
 conversion_impls!(I256, U256, I320, U320);
 egcd_impls!(I320, U256, I256);
-modinv_impls!(I256);
+modinv_impls!(U256, I320, U320);
 add_impls!(I320, I384, U384);
 signed_impls!(I320, U320);
 cmp_impls!(I320);
@@ -19,7 +19,7 @@ conversion_impls!(I320, U320, I384, U384);
 signed_impls!(I384, U384);
 conversion_impls!(I384, U384, I448, U448);
 egcd_impls!(I448, U384, I384);
-modinv_impls!(I384);
+modinv_impls!(U384, I448, U448);
 add_impls!(I448, I512, U512);
 signed_impls!(I448, U448);
 cmp_impls!(I448);
@@ -29,7 +29,7 @@ conversion_impls!(I448, U448, I512, U512);
 signed_impls!(I512, U512);
 conversion_impls!(I512, U512, I576, U576);
 egcd_impls!(I576, U512, I512);
-modinv_impls!(I512);
+modinv_impls!(U512, I576, U576);
 add_impls!(I576, I640, U640);
 signed_impls!(I576, U576);
 cmp_impls!(I576);
@@ -37,7 +37,7 @@ shift_impls!(I576, U576);
 subtraction_impls!(I576, I640, U640);
 conversion_impls!(I576, U576, I640, U640);
 egcd_impls!(I640, U576, I576);
-modinv_impls!(I576);
+modinv_impls!(U576, I640, U640);
 add_impls!(I640, I704, U704);
 signed_impls!(I640, U640);
 cmp_impls!(I640);
@@ -48,7 +48,7 @@ signed_impls!(I704, U704);
 signed_impls!(I1024, U1024);
 conversion_impls!(I1024, U1024, I1088, U1088);
 egcd_impls!(I1088, U1024, I1024);
-modinv_impls!(I1024);
+modinv_impls!(U1024, I1088, U1088);
 add_impls!(I1088, I1152, U1152);
 signed_impls!(I1088, U1088);
 cmp_impls!(I1088);
@@ -59,7 +59,7 @@ signed_impls!(I1152, U1152);
 signed_impls!(I2048, U2048);
 conversion_impls!(I2048, U2048, I2112, U2112);
 egcd_impls!(I2112, U2048, I2048);
-modinv_impls!(I2048);
+modinv_impls!(U2048, I2112, U2112);
 add_impls!(I2112, I2176, U2176);
 signed_impls!(I2112, U2112);
 cmp_impls!(I2112);
@@ -70,7 +70,7 @@ signed_impls!(I2176, U2176);
 signed_impls!(I3072, U3072);
 conversion_impls!(I3072, U3072, I3136, U3136);
 egcd_impls!(I3136, U3072, I3072);
-modinv_impls!(I3072);
+modinv_impls!(U3072, I3136, U3136);
 add_impls!(I3136, I3200, U3200);
 signed_impls!(I3136, U3136);
 cmp_impls!(I3136);
@@ -81,7 +81,7 @@ signed_impls!(I3200, U3200);
 signed_impls!(I4096, U4096);
 conversion_impls!(I4096, U4096, I4160, U4160);
 egcd_impls!(I4160, U4096, I4096);
-modinv_impls!(I4096);
+modinv_impls!(U4096, I4160, U4160);
 add_impls!(I4160, I4224, U4224);
 signed_impls!(I4160, U4160);
 cmp_impls!(I4160);
@@ -92,7 +92,7 @@ signed_impls!(I4224, U4224);
 signed_impls!(I7680, U7680);
 conversion_impls!(I7680, U7680, I7744, U7744);
 egcd_impls!(I7744, U7680, I7680);
-modinv_impls!(I7680);
+modinv_impls!(U7680, I7744, U7744);
 add_impls!(I7744, I7808, U7808);
 signed_impls!(I7744, U7744);
 cmp_impls!(I7744);
@@ -103,7 +103,7 @@ signed_impls!(I7808, U7808);
 signed_impls!(I8192, U8192);
 conversion_impls!(I8192, U8192, I8256, U8256);
 egcd_impls!(I8256, U8192, I8192);
-modinv_impls!(I8192);
+modinv_impls!(U8192, I8256, U8256);
 add_impls!(I8256, I8320, U8320);
 signed_impls!(I8256, U8256);
 cmp_impls!(I8256);
@@ -114,7 +114,7 @@ signed_impls!(I8320, U8320);
 signed_impls!(I15360, U15360);
 conversion_impls!(I15360, U15360, I15424, U15424);
 egcd_impls!(I15424, U15360, I15360);
-modinv_impls!(I15360);
+modinv_impls!(U15360, I15424, U15424);
 add_impls!(I15424, I15488, U15488);
 signed_impls!(I15424, U15424);
 cmp_impls!(I15424);
@@ -305,11 +305,11 @@ mod tests {
     generate_modinv_tests!(I512, U512, i512);
     generate_modinv_tests!(I576, U576, i576);
     generate_modinv_tests!(I1024, U1024, i1024);
-    generate_modinv_tests!(I2048, U2048, i2048);
-    generate_modinv_tests!(I3072, U3072, i3072);
-    generate_modinv_tests!(I4096, U4096, i4096);
-    generate_modinv_tests!(I7680, U7680, i7680);
-    generate_modinv_tests!(I8192, U8192, i8192);
+    generate_modinv_tests!(ignore I2048, U2048, i2048);
+    generate_modinv_tests!(ignore I3072, U3072, i3072);
+    generate_modinv_tests!(ignore I4096, U4096, i4096);
+    generate_modinv_tests!(ignore I7680, U7680, i7680);
+    generate_modinv_tests!(ignore I8192, U8192, i8192);
     generate_modinv_tests!(ignore I15360, U15360, i15360);
   }
 }

src/signed/mod.rs

@@ -23,5 +23,6 @@ use std::ops::{Sub,SubAssign};
 use unsigned::*;
 
 pub use self::egcd::EGCD;
+pub use self::modinv::ModInv;
 
 include!("invoc.rs");

src/signed/modinv.rs

@@ -1,14 +1,59 @@
+pub trait ModInv: Sized {
+    fn modinv(&self, phi: &Self) -> Option<Self>;
+}
+
 macro_rules! modinv_impls {
-    ($sname: ident) => {
+    ($name: ident, $sname: ident, $uname: ident) => {
+        impl ModInv for $name {
+            fn modinv(&self, phi: &$name) -> Option<$name>
+            {
+                let (_, mut b, g) = phi.egcd(&self);
+
+                if g != $sname::from(1i64) {
+                    return None;
+                }
+
+                while b.is_negative() {
+                    b += $sname::from($uname::from(phi));
+                }
+
+                Some($name::from($uname::from(b)))
+            }
+        }
     };
 }
 
 #[cfg(test)]
 macro_rules! generate_modinv_tests {
     ($sname: ident, $tname: ident, $mname: ident) => {
+        #[test]
+        fn $mname() {
+            generate_modinv_tests!(body $sname, $tname, $mname);
+        }
     };
     (ignore $sname: ident, $tname: ident, $mname: ident) => {
+        #[test]
+        #[ignore]
+        fn $mname() {
+            generate_modinv_tests!(body $sname, $tname, $mname);
+        }
     };
     (body $sname: ident, $tname: ident, $mname: ident) => {
+        let fname = format!("testdata/modinv/{}.tests", stringify!($sname));
+        run_test(fname.to_string(), 3, |case| {
+            let (nega, abytes) = case.get("a").unwrap();
+            let (negb, bbytes) = case.get("b").unwrap();
+            let (negc, cbytes) = case.get("c").unwrap();
+
+            assert!(!nega && !negb && !negc);
+            let a = $tname::from_bytes(abytes);
+            let b = $tname::from_bytes(bbytes);
+            let c = $tname::from_bytes(cbytes);
+
+            match a.modinv(&b) {
+                None      => assert!(false),
+                Some(myc) => assert_eq!(c, myc)
+            }
+        });
     };
 }