Can tail recursion apply to this code? - c++

Question

I have a simple piece of code, that addresses this (poorly stated, out of place) question :
template<typename It>
bool isAlpha(It first, It last)
{
return (first != last && *first != '\0') ?
(isalpha(static_cast<int>(*first)) && isAlpha(++first, last)) : true;
}
I'm trying to figure out how can I go about implementing it in a tail recursive fashion, and although there are great sources like this answer, I can't wrap my mind around it.
Can anyone help ?
EDIT
I'm placing the disassembly code below; The compiler is gcc 4.9.0 compiling with -std=c++11 -O2 -Wall -pedantic the assembly output is
bool isAlpha<char const*>(char const*, char const*):
cmpq %rdi, %rsi
je .L5
movzbl (%rdi), %edx
movl $1, %eax
testb %dl, %dl
je .L12
pushq %rbp
pushq %rbx
leaq 1(%rdi), %rbx
movq %rsi, %rbp
subq $8, %rsp
.L3:
movsbl %dl, %edi
call isalpha
testl %eax, %eax
jne .L14
xorl %eax, %eax
.L2:
addq $8, %rsp
popq %rbx
popq %rbp
.L12:
rep ret
.L14:
cmpq %rbp, %rbx
je .L7
addq $1, %rbx
movzbl -1(%rbx), %edx
testb %dl, %dl
jne .L3
.L7:
movl $1, %eax
jmp .L2
.L5:
movl $1, %eax
ret

Answer 1

To clarify cdhowie's point, the function can be rewritten as follows (unless I made a mistake):
bool isAlpha(It first, It last)
{
if (first == last)
return true;
if (*first == '\0')
return true;
if (!isalpha(static_cast<int>(*first))
return false;
return isAlpha(++first, last);
}
Which would indeed allow for trivial tail call elimination.
This is normally a job for the compiler, though.