Revert "implemented rv64. did not use intrinsics due to [this issue](rust-lang/stdarch#1453 (comment))"

This reverts commit 660197d.

Author: sayantn

README.md

@@ -1,31 +1,29 @@
 This is a pure-Rust platform-agnostic [AES](https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197-upd1.pdf) library, that
 is focused on reusability and optimal performance.
 
-This library guarantees the best performance on the `target-cpu` (if correctly specified). This currently has 6
-implementations, among which it automatically decides the best (most performant) using Cargo's `target-feature` flags.
+This library guarantees the best performance on the `target_cpu` (if correctly specified). This currently has 5
+implementations, among which it automatically decides the best (most performant) using Cargo's `target_feature` flags.
 
 # The implementations and their requirements are:
 
 - AES-NI (with Vector AES for 2- and 4- blocks) => requires a Nightly Compiler, the `nightly` feature to be enabled, and
-  compiling for x86(64) with the `avx512f` and `vaes` target-feature flags set.
+  compiling for x86(64) with the `avx512f` and `vaes` target_feature flags set.
 - AES-NI (with Vector AES for 2-blocks) => requires a Nightly Compiler, the `nightly` feature to be enabled, and
-  compiling for x86(64) with the `vaes` target-feature flag set. (although `vaes` is a AVX-512 feature, some AlderLake
+  compiling for x86(64) with the `vaes` target_feature flag set. (although `vaes` is a AVX-512 feature, some AlderLake
   CPUs have `vaes` without AVX-512 support)
-- AES-NI => requires compiling for x86(64) with the `sse4.1` and `aes` target-feature flags set.
-- AES-Neon => requires compiling for AArch64 or ARM64EC or ARM-v8 with the `aes` target-feature flag set (ARM-v8
+- AES-NI => requires compiling for x86(64) with the `sse4.1` and `aes` target_feature flags set.
+- AES-Neon => requires compiling for AArch64 or ARM64EC or ARM-v8 with the `aes` target_feature flag set (ARM-v8
   requires a Nightly compiler and the `nightly` feature to be enabled) .
-- AES-RV64 => requires a Nightly compiler, the `nightly` feature to be enabled, and compiling for RISC-V RV64 with
-  the `zkne` and `zknd` target-feature flags set.
 - Software AES => fallback implementation based on Rijmen and Daemen's `optimized` implementation (available
   on [their website](https://web.archive.org/web/20050828204927/http://www.iaik.tu-graz.ac.at/research/krypto/AES/old/%7Erijmen/rijndael/))
 
-If you are unsure about the target-feature flags to set, use `target-cpu=native` (if not cross-compiling) in
+If you are unsure about the target_feature flags to set, use `target_cpu=native` (if not cross-compiling) in
 the `RUSTFLAGS` environment variable, and use the `nightly` feature only if you are using a nightly compiler.
 
 # Warning
 
-Using the wrong `target-feature` flags may lead to the binary crashing due to an "Unknown Instruction" error. This
-library uses these flags to use the CPU intrinsics to maximize performance. If you are unsure what `target-feature`s are
+Using the wrong `target_feature` flags may lead to the binary crashing due to an "Unknown Instruction" error. This
+library uses these flags to use the CPU intrinsics to maximize performance. If you are unsure what `target_feature`s are
 supported on your CPU, use the command
 
 ````bash

src/aes_riscv64.rs

@@ -43,15 +43,6 @@ cfg_if! {
         mod aes_arm;
         pub use aes_arm::AesBlock;
         use aes_arm::*;
-    } else if #[cfg(all(
-        feature = "nightly",
-        target_arch = "riscv64",
-        target_feature = "zkne",
-        target_feature = "zknd"
-    ))] {
-        mod aes_riscv64;
-        pub use aes_riscv64::AesBlock;
-        use aes_riscv64::*;
     } else {
         mod aes_default;
         pub use aes_default::AesBlock;