Seek help for the mixed compilation of c and assembly

For the mixed compilation of c and assembly-Linux general technology-Linux programming and kernel information, see the following for details. Another problem encountered during graduation project
First look at the code

# Include

Void _ delay (int loops)
{
Long dummy;
_ Asm _ volatile _ ("gettr" _ t0 ", % 1 \ n \ t"
"_ Pta 4," _ t0 "\ n \ t"
"Addi % 0,-1, % 0 \ n \ t"
"Bne % 0, r63," _ t0 "\ n \ t"

"Ptabs % 1," _ t0 "\ n \ t": "= r" (loops ),
"= R" (dummy)
: "0" (loops ));
}

Void _ udelay (unsigned long usecs, unsigned long lpj)
{
Usecs * = (unsigned long) HZ <32)/1000000) * lpj;
_ Delay (long) usecs> 32 );
}

# Ifdef notdef
# Define mdelay (n )(\
{Unsigned long msec = (n); while (msec --) udelay (1000 );})
# Else
# Define mdelay (n )(\
(_ Builtin_constant_p (n) & (n) <= MAX_UDELAY_MS )? Udelay (n) * 1000 ):\
({Unsigned long msec = (n); while (msec --) udelay (1000 );}))
# Endif


This is a mix of C and assembler functions.
Understand that it uses at&t's Assembly format. I have also read the introduction of this format,
For example, _ pta 4 and bne r63 still do not understand what it means.

Can you use related materials.
Thank you!