converting to unsigned 16 bit integers in julia

64to16.jl

# converting from Int64 to UInt16 in Julia can result in a minefield of inexacterrors,
# which could be performance-debilitating (if you care about that).

code_native(Int16, (Int64,))  

# ==>(edited)
#  pushq  %rbp
#  movq   %rsp, %rbp
#  movswq %si, %rax
#  cmpq   %rsi, %rax
#  jne    L22
#  movw   %si, %ax
#  popq   %rbp
#  ret
#  L22:	
#  movabsq  $jl_inexact_exception, %rax
#  movq	    (%rax), %rdi
#  movabsq  $jl_throw, %rax
#  callq    *%rax

# unlike array bounds-checking, with the @inbounds macro, integer conversions do not have
# a simple macro which takes care of this problem.  In order to eliminate the checking, 
# you have to add extraneous information which will create static-analysis guarantees 
# that the desired result is in-range (even if your code is set up so that can't happen).

to16(n::Int64) = UInt16(reinterpret(UInt64, n) & 0x0000_0000_0000_FFFF)

code_native(to16, (Int64,)) 

# ==>(edited)
#  pushq %rbp
#  movq  %rsp, %rbp
#  movw  %di, %ax
#  popq  %rbp
#  ret

# this is optimized to one line of code! (movw	%di, %ax), and may even be inlined.