Routines
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13545: THE 'TEST-ZERO' SUBROUTINE
Used by the routines at IF_CMD, PREP_M_D, negate, sgn, greater_0, f_not, no_or_no, no_and_no and str_no.
This subroutine is called at least nine times to test whether a floating-point number is zero. This test requires that the first four bytes of the number should each be zero. The subroutine returns with the carry flag set if the number was in fact zero.
Input
HL Address of the first byte of the number
Output
F Carry flag set if the number is zero
TEST_ZERO 13545 PUSH HL Save HL on the stack.
13546 PUSH BC Save BC on the stack.
13547 LD B,A Save the value of A in B.
13548 LD A,(HL) Get the first byte.
13549 INC HL Point to the second byte.
13550 OR (HL) 'OR' the first byte with the second.
13551 INC HL Point to the third byte.
13552 OR (HL) 'OR' the result with the third byte.
13553 INC HL Point to the fourth byte.
13554 OR (HL) 'OR' the result with the fourth byte.
13555 LD A,B Restore the original value of A.
13556 POP BC And of BC.
13557 POP HL Restore the pointer to the number to HL.
13558 RET NZ Return with carry reset if any of the four bytes was non-zero.
13559 SCF Set the carry flag to indicate that the number was zero, and return.
13560 RET
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