Add bitwise shifts to Quil

grammars/Quil.g4

@@ -98,7 +98,7 @@ offsetDescriptor    : OFFSET INT IDENTIFIER ;
 
 classicalUnary      : ( NEG | NOT | TRUE | FALSE ) addr ;
 classicalBinary     : logicalBinaryOp | arithmeticBinaryOp | move | exchange | convert ;
-logicalBinaryOp     : ( AND | OR | IOR | XOR ) addr ( addr | INT ) ;
+logicalBinaryOp     : ( AND | OR | IOR | XOR | SHL | SHR | ASHR ) addr ( addr | INT ) ;
 arithmeticBinaryOp  : ( ADD | SUB | MUL | DIV ) addr ( addr | number ) ;
 move                : MOVE addr ( addr | number );
 exchange            : EXCHANGE addr addr ;
@@ -184,6 +184,9 @@ FALSE               : 'FALSE' ; // Deprecated
 AND                 : 'AND' ;
 IOR                 : 'IOR' ;
 XOR                 : 'XOR' ;
+SHL                 : 'SHL' ;
+SHR                 : 'SHR' ;
+ASHR                : 'ASHR' ;
 OR                  : 'OR' ;   // Deprecated
 
 ADD                 : 'ADD' ;

specgen/spec/sec-mem.s

@@ -475,6 +475,7 @@ the same syntax.}
 @syntax[:name "Classical Binary"]{
          MOVE @alt EXCHANGE @alt CONVERT
     @alt AND @alt IOR @alt XOR
+    @alt SHL @alt SHR @alt ASHR
     @alt ADD @alt SUB @alt MUL @alt DIV
 }
 
@@ -582,6 +583,30 @@ XOR      a b            # a := a ^ b
          <bit> <bit>
          <bit> <!int>
 
+# Bitshifts
+#
+# - Shifting by a negative number of bits is forbidden.
+#
+# - Shifting by as many or more bits than are present in a word fills
+#   the entire word with the bit being shifted in.
+#
+# - SHL and SHR are "logical shifts", and fill in the shifted-out bits
+#   with zeros.
+#
+# - ASHR is an "arithmetic shift", and is the same as n := n * 2⁻ᵏ
+#   (rounding towards -∞); in a 2's-complement representation, this is
+#   the same as shifting right and filling in the shifted-out bits
+#   with the original value of the high bit.
+SHL      n b            # n := n << b; shift left (logical)
+SHR      n b            # n := n >> b; shift right (logical)
+ASHR     n b            # n := n * 2⁻ᵏ, or n := n >>> b; arithmetic shift right
+         <oct> <oct>
+         <oct> <int>
+         <oct> <!int>
+         <int> <oct>
+         <int> <int>
+         <int> <!int>
+
 # Arithmetic Operations
 NEG      a              # a := -a
          <int>

specgen/spec/sec-structure.s

@@ -161,13 +161,11 @@ i pi
 
 @p{The following identifiers are reserved (as Quil keywords):
 
-@clist{
-ADD AND AS CONTROLLED CONVERT DAGGER DECLARE DEFCIRCUIT DEFGATE DIV EQ
-EXCHANGE FORKED GE GT HALT INCLUDE IOR JUMP JUMP-UNLESS JUMP-WHEN
-LABEL LE LOAD LT MATRIX MEASURE MOVE MUL NEG NOP NOT OFFSET PAULI-SUM
-PERMUTATION PRAGMA RESET SHARING STORE SUB WAIT XOR EXTERN CALL
-}
-}
+@clist{ ADD AND ASHR AS CONTROLLED CONVERT DAGGER DECLARE DEFCIRCUIT
+DEFGATE DIV EQ EXCHANGE FORKED GE GT HALT INCLUDE IOR JUMP JUMP-UNLESS
+JUMP-WHEN LABEL LE LOAD LT MATRIX MEASURE MOVE MUL NEG NOP NOT OFFSET
+PAULI-SUM PERMUTATION PRAGMA RESET SHARING SHL SHR STORE SUB WAIT XOR
+EXTERN CALL } }
 
 @p{The following identifiers are also reserved (for standard gate
 definitions):