acle: move arm/dsp into acle/{dsp,simd32}

addresses #557 (comment)

crates/core_arch/src/acle/dsp.rs

@@ -4,18 +4,45 @@
 //!
 //! Intrinsics that could live here:
 //!
-//! - __smulbb
-//! - __smulbt
-//! - __smultb
-//! - __smultt
-//! - __smulwb
-//! - __smulwt
-//! - __qadd
-//! - __qsub
-//! - __qdbl
-//! - __smlabb
-//! - __smlabt
-//! - __smlatb
-//! - __smlatt
-//! - __smlawb
-//! - __smlawt
+//! - [ ] __smulbb
+//! - [ ] __smulbt
+//! - [ ] __smultb
+//! - [ ] __smultt
+//! - [ ] __smulwb
+//! - [ ] __smulwt
+//! - [x] __qadd
+//! - [x] __qsub
+//! - [ ] __qdbl
+//! - [ ] __smlabb
+//! - [ ] __smlabt
+//! - [ ] __smlatb
+//! - [ ] __smlatt
+//! - [ ] __smlawb
+//! - [ ] __smlawt
+
+extern "C" {
+    #[link_name = "llvm.arm.qadd"]
+    fn arm_qadd(a: i32, b: i32) -> i32;
+
+    #[link_name = "llvm.arm.qsub"]
+    fn arm_qsub(a: i32, b: i32) -> i32;
+
+}
+
+/// Signed saturating addition
+///
+/// Returns the 32-bit saturating signed equivalent of a + b.
+#[inline]
+#[cfg_attr(test, assert_instr(qadd))]
+pub unsafe fn qadd(a: i32, b: i32) -> i32 {
+    arm_qadd(a, b)
+}
+
+/// Signed saturating subtraction
+///
+/// Returns the 32-bit saturating signed equivalent of a - b.
+#[inline]
+#[cfg_attr(test, assert_instr(qsub))]
+pub unsafe fn qsub(a: i32, b: i32) -> i32 {
+    arm_qsub(a, b)
+}