The instructions of this group are 'jump' or 'discrimination' instructions. With function-numbers 60 to 65 a comparison is made between the signed 48-bit numbers y and z while with function-numbers 66 and 67 the comparison is between pY and z. (In 2-address form z = 0 for all function-numbers). Depending on the result of this comparison the next instruction obeyed is either that stored in register X or the one stored in the next-higher numbered register to that containing the 'jump' instruction itself. This is achieved by arranging for the control-number either to be set to X (strictly, to the machine-address represented by X, which may be a Basic or a Symbolic Address) or to be increased by unity from its current value.
The replacement and modification facilities operate in the normal way; in particular the destination address X may be replaced and/or modified. Such treatment of the X-address yields a 'switch', that is, a single instruction which causes the computer to follow one or another of several possible courses of action, depending on the result of a comparison between two numbers and on the value of a third number (a modifier). Note that when a jump instruction does not cause a jump, the destination address is not checked for lock-outs or reservations, unless replaced.
Function number 60 [0110 000]
3-address: Jump to X if y = z 2-address: Jump to X if y=0.
Function number 61 [0110 001]
3-address: Jump to X if y ≠ z 2-address: Jump to X if y≠0.
Function number 62 [0110 010]
Jump to X if y > z (i.e. z < y)
2-address: Jump to X if y > 0 (i.e. y positive)
Function number 63 [0110 011]
Jump to X if y ¬>
z (i.e. z ≥
2-address: Jump to X if y ¬>0 (i.e. y negative or zero).
Function number 64 [0110 100]
Jump to X if y < z (i.e. z ≥
2-address: Jump to X if y < 0 (i.e. y negative, ys=1)
Function number 65 [0110 101]
3-address: Jump to X if y ¬< z ( i.e. z ≤ y)
2-address: Jump to X if y ¬< 0 (i.e. y non-negative, ys = 0)
Function number 66 [0110 110]
3-address: Jump to X if pY = z
2-address: Jump to X if pY = 0
Although pY can be the content of any of the pseudo-registers, the most common use of this instruction is to test the state of the overflow indicator, by reference to P4, P5, P6 or P7.
Function number 67 [0110 111]
3-address: Jump to X if pY ≠ z
2-address: Jump to X if pY ≠ 0.
See comment under function-number 66.