13.17 grow (4136)

The parameter, “sp”, of this procedure defines the address of a word which should be included in the user mode stack.

4141:

If the stack already extends far enough, simply return with a zero value.

Note that this test relies on the idiosyncrasies of 2’s complement arithmetic, and if both

|sp|

and

|u.u_size |

the decision to extend the stack may be taken wrongly at this juncture;

4143:

Calculate the stack size increment needed to include the new stack point plus a 20*32 word margin;

4144:

Check that this value is in fact positive (i.e. we are not dealing with a failure of the test on line 4141.);

4146:

Check that the new stack size does not conflict with the memory segmentation constraints (“estabur” sets “u.u_error” if they do) and reset the segmentation register prototypes;

4148:

Get a new, enlarged data area, copy the stack segments (32 words at a time) into the high end of the new data area, and clear the segments which now become the stack expansion;

4156:

Update the stack size, “u.u_ssize” and return a “successful” result.