Add two numbers

Problem

Add two values stored in data labels and print the sum. (Reading decimal numbers from stdin is more involved — there is no bit.input_dec in the STL; you’d hand-roll one using bit.input + per-digit parsing. This recipe sticks to compile-time values for clarity.)

Code

stl.startup_and_init_all

bit.print_str 7, label_a
bit.print_dec_uint 32, a
stl.output '\n'

bit.print_str 7, label_b
bit.print_dec_uint 32, b
stl.output '\n'

bit.add 32, a, b      // a += b

bit.print_str 7, label_sum
bit.print_dec_uint 32, a
stl.output '\n'
stl.loop

label_a:   bit.str "a   = "
label_b:   bit.str "b   = "
label_sum: bit.str "a+b = "
a: bit.vec 32, 123
b: bit.vec 32, 456

Output:

a   = 123
b   = 456
a+b = 579

Walkthrough

  • bit.vec 32, val allocates a 32-bit variable initialised to val. The initial value is baked into the macro expansion at assembly time.

  • bit.add n, dst, src — adds src[:n] into dst[:n] in place. Result lives in dst. The macro propagates the carry naturally.

  • bit.print_dec_uint 32, a — print a (now holding a+b).

Variations

Hex for less-expensive arithmetic:

hex.add 8, dst, src

Subtraction:

bit.sub 32, a, b      // a -= b

Multiplication:

bit.mul 16, dst, x       // dst *= x (both 16-bit)

See also