[abm] support popcnt and lzcnt

library/stdarch/src/x86/abm.rs

@@ -0,0 +1,71 @@
+//! Advanced Bit Manipulation (ABM) instructions
+//! 
+//! That is, POPCNT and LZCNT. These instructions have their own CPUID bits to
+//! indicate support.
+//!
+//! TODO: it is unclear which target feature to use here. SSE4.2 should be good
+//! enough but we might need to use BMI for LZCNT if there are any problems.
+//!
+//! The references are:
+//!
+//! - [Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2: Instruction Set Reference, A-Z](http://www.intel.de/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf).
+//! - [AMD64 Architecture Programmer's Manual, Volume 3: General-Purpose and System Instructions](http://support.amd.com/TechDocs/24594.pdf).
+//!
+//! [Wikipedia](https://en.wikipedia.org/wiki/Bit_Manipulation_Instruction_Sets#ABM_.28Advanced_Bit_Manipulation.29)
+//! provides a quick overview of the instructions available.
+
+
+/// Counts the leading most significant zero bits.
+///
+/// When the operand is zero, it returns its size in bits.
+#[inline(always)]
+#[target_feature = "+sse4.2"]
+pub fn _lzcnt_u32(x: u32) -> u32 { x.leading_zeros() }
+
+/// Counts the leading most significant zero bits.
+///
+/// When the operand is zero, it returns its size in bits.
+#[inline(always)]
+#[target_feature = "+sse4.2"]
+pub fn _lzcnt_u64(x: u64) -> u64 { x.leading_zeros() as u64 }
+
+/// Counts the bits that are set.
+#[inline(always)]
+#[target_feature = "+sse4.2"]
+pub fn _popcnt32(x: u32) -> u32 { x.count_ones() }
+
+/// Counts the bits that are set.
+#[inline(always)]
+#[target_feature = "+sse4.2"]
+pub fn _popcnt64(x: u64) -> u64 { x.count_ones() as u64 }
+
+#[cfg(all(test, target_feature = "sse4.2", any(target_arch = "x86", target_arch = "x86_64")))]
+mod tests {
+    use x86::abm;
+
+    #[test]
+    #[target_feature = "+sse4.2"]
+    fn _lzcnt_u32() {
+        assert_eq!(abm::_lzcnt_u32(0b0101_1010u32), 25u32);
+    }
+
+    #[test]
+    #[target_feature = "+sse4.2"]
+    fn _lzcnt_u64() {
+        assert_eq!(abm::_lzcnt_u64(0b0101_1010u64), 57u64);
+    }
+
+    #[test]
+    #[target_feature = "+sse4.2"]
+    fn _popcnt32() {
+        assert_eq!(abm::_popcnt32(0b0101_1010u32), 4);
+    }
+
+    #[test]
+    #[target_feature = "+sse4.2"]
+    fn _popcnt64() {
+        assert_eq!(abm::_popcnt64(0b0101_1010u64), 4);
+    }
+}
+
+

library/stdarch/src/x86/mod.rs

@@ -20,5 +20,6 @@
 mod avx;
 mod avx2;
 
+mod abm;
 mod bmi;
 mod bmi2;