Fix BigInteger.remainder check and BigInteger TODOsHEADlineage-18.1

Restore the BigInteger.remainder fallback test to check for small
results. Use RemainderKnuth if either the divisor or result is
short, as was done before. Checking for a short dividend doesn't
really make much sense, since that makes the result short as well.

Failed BN context allocations used to just pass null to the next
operation. Looking at the BN_mul implementation, it doesn't appear
that ends well. Explicitly check for that case.

Remove some potentially useful but unused methods from NativeBN.

Bug: 163898786
Test: Build and boot AOSP
Change-Id: I97a46199d8cf69acf29bcfc2f614c2205ff16262

2 files changed, 6 insertions, 30 deletions

diff --git a/luni/src/main/java/libcore/math/NativeBN.java b/luni/src/main/java/libcore/math/NativeBN.java
index fb1cb78a50..8b2ea0f1ee 100644
--- a/luni/src/main/java/libcore/math/NativeBN.java
+++ b/luni/src/main/java/libcore/math/NativeBN.java
@@ -14,9 +14,6 @@
  * limitations under the License.
  */
 
-// TODO: Prune out the methods we no longer need after replacing the BigInteger
-// code.
-
 package libcore.math;
 
 /**
@@ -36,13 +33,6 @@ public final class NativeBN {
     // word at index 0.
     public static native int[] bn2litEndInts(long a);
 
-    public static native int sign(long a);
-    // Returns -1, 0, 1 AND NOT boolean.
-    // #define BN_is_negative(a) ((a)->neg != 0)
-
-    public static native void BN_set_negative(long b, int n);
-    // void BN_set_negative(BIGNUM *b, int n);
-
     public static native void BN_mul(long r, long a, long b);
     // int BN_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
 
diff --git a/luni/src/main/native/libcore_math_NativeBN.cpp b/luni/src/main/native/libcore_math_NativeBN.cpp
index a123014bc5..dc4b947358 100644
--- a/luni/src/main/native/libcore_math_NativeBN.cpp
+++ b/luni/src/main/native/libcore_math_NativeBN.cpp
@@ -14,8 +14,6 @@
  * limitations under the License.
  */
 
-// TODO: Check that we handle context allocation failures correctly.
-
 #define LOG_TAG "NativeBN"
 
 #include <stdio.h>
@@ -142,36 +140,26 @@ static jintArray NativeBN_bn2litEndInts(JNIEnv* env, jclass, jlong a0) {
   return result;
 }
 
-static int NativeBN_sign(JNIEnv*, jclass, jlong a) {
-  if (BN_is_zero(toBigNum(a))) {
-      return 0;
-  } else if (BN_is_negative(toBigNum(a))) {
-    return -1;
-  }
-  return 1;
-}
-
-static void NativeBN_BN_set_negative(JNIEnv*, jclass, jlong b, int n) {
-  BN_set_negative(toBigNum(b), n);
-}
-
 static void NativeBN_BN_mul(JNIEnv* env, jclass, jlong r, jlong a, jlong b) {
   Unique_BN_CTX ctx(BN_CTX_new());
-  if (!BN_mul(toBigNum(r), toBigNum(a), toBigNum(b), ctx.get())) {
+  BN_CTX* ctxp = ctx.get();
+  if (!ctxp || !BN_mul(toBigNum(r), toBigNum(a), toBigNum(b), ctxp)) {
     throwException(env);
   }
 }
 
 static void NativeBN_BN_div(JNIEnv* env, jclass, jlong q, jlong rem, jlong num, jlong divisor) {
   Unique_BN_CTX ctx(BN_CTX_new());
-  if (!BN_div(toBigNum(q), toBigNum(rem), toBigNum(num), toBigNum(divisor), ctx.get())) {
+  BN_CTX* ctxp = ctx.get();
+  if (!ctxp || !BN_div(toBigNum(q), toBigNum(rem), toBigNum(num), toBigNum(divisor), ctxp)) {
     throwException(env);
   }
 }
 
 static void NativeBN_BN_mod_exp(JNIEnv* env, jclass, jlong r, jlong a, jlong p, jlong m) {
   Unique_BN_CTX ctx(BN_CTX_new());
-  if (!BN_mod_exp(toBigNum(r), toBigNum(a), toBigNum(p), toBigNum(m), ctx.get())) {
+  BN_CTX* ctxp = ctx.get();
+  if (!ctxp || !BN_mod_exp(toBigNum(r), toBigNum(a), toBigNum(p), toBigNum(m), ctxp)) {
     throwException(env);
   }
 }
@@ -182,10 +170,8 @@ static JNINativeMethod gMethods[] = {
    NATIVE_METHOD(NativeBN, BN_mod_exp, "(JJJJ)V"),
    NATIVE_METHOD(NativeBN, BN_mul, "(JJJ)V"),
    NATIVE_METHOD(NativeBN, BN_new, "()J"),
-   NATIVE_METHOD(NativeBN, BN_set_negative, "(JI)V"),
    NATIVE_METHOD(NativeBN, bn2litEndInts, "(J)[I"),
    NATIVE_METHOD(NativeBN, litEndInts2bn, "([IIZJ)V"),
-   NATIVE_METHOD(NativeBN, sign, "(J)I"),
 };
 void register_libcore_math_NativeBN(JNIEnv* env) {
     jniRegisterNativeMethods(env, "libcore/math/NativeBN", gMethods, NELEM(gMethods));