The routine at STACK_A continues here.
This subroutine gives the floating-point form for the absolute binary value currently held in the BC register pair.
The form used in this and hence in the two previous subroutines as well is the one reserved in the Spectrum for small integers n, where -65535<=n<=65535. The first and fifth bytes are zero; the third and fourth bytes are the less significant and more significant bytes of the 16 bit integer n in two's complement form (if n is negative, these two bytes hold 65536+n); and the second byte is a sign byte, +00 for '+' and +FF for '-'.
|Re-initialise IY to ERR-NR.
|Clear the A register.
|And the E register, to indicate '+'.
|Copy the less significant byte to D.
|And the more significant byte to C.
|Clear the B register.
|Now stack the number.
|Use the calculator to make HL point to STKEND-5.
|Clear the carry flag.