One thing that might be useful to me if you have the time, is an assembler dump of the sources. Can gcc do that?

gcc -S a.c
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And if it can, would it show the actual operations involved, or just calls to system library routines?

It provides the assembler code for the code you are compiling, which would include inlined functions, but I don't see why it would disassemble existing objects.

$ cat a.c
#include <stdio.h>

int main() {
   printf("Hello, World!\n");
   return 0;
}
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$ cat a.s
        .file   "a.c"
        .section        .rodata
.LC0:
        .string "Hello, World!"
        .text
.globl main
        .type   main, @function
main:
        leal    4(%esp), %ecx
        andl    $-16, %esp
        pushl   -4(%ecx)
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %ecx
        subl    $4, %esp
        movl    $.LC0, (%esp)
        call    puts
        movl    $0, %eax
        addl    $4, %esp
        popl    %ecx
        popl    %ebp
        leal    -4(%ecx), %esp
        ret
        .size   main, .-main
        .ident  "GCC: (Debian 4.3.2-1.1) 4.3.2"
        .section        .note.GNU-stack,"",@progbits
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Are they inlined?

I can't try to install the dev gcc needed for Math::Int128 at this moment.