Clarify bit fiddling names.

ykrt/src/compile/jitc_yk/jit_ir.rs

@@ -18,13 +18,18 @@ const OPCODE_SIZE: u64 = 8;
 /// Max number of operands in a short instruction.
 const SHORT_INSTR_MAX_OPERANDS: u64 = 3;
 
-/// Bit fiddling for a short operands.
+/// Bit fiddling.
+///
+/// In the constants below:
+///  - `*_SIZE`: the size of a field in bits.
+///  - `*_MASK`: a mask with one bits occupying the field in question.
+///
+/// Bit fiddling for a short operands:
 const SHORT_OPERAND_SIZE: u64 = 18;
 const SHORT_OPERAND_KIND_SIZE: u64 = 3;
 const SHORT_OPERAND_KIND_MASK: u64 = 7;
 const SHORT_OPERAND_VALUE_SIZE: u64 = 15;
 const SHORT_OPERAND_MASK: u64 = 0x3ffff;
-
 /// Bit fiddling for instructions.
 const INSTR_ISSHORT_SIZE: u64 = 1;
 const INSTR_ISSHORT_MASK: u64 = 1;