This is part of Family API which allow to create dual-os version of program runs under OS/2 and DOS

Note: This is legacy API call. It is recommended to use 32-bit equivalent

2021/09/17 04:47 · prokushev · 0 Comments
2021/08/20 03:18 · prokushev · 0 Comments


This call returns a shift count used to derive the selectors that address memory allocated with DosAllocHuge.


DosGetHugeShift (ShiftCount)


  • ShiftCount (PUSHORT) - output : Address of the shift count.

Return Code

rc (USHORT) - return

Return code description is:

  • 0 NO_ERROR


Each segment of a huge memory allocation has a unique selector. To compute the next sequential selector in a huge memory area, take the value 1, shift it left by the number of bits specified in shift count. Use the resulting value as an increment to add to the previous selector (using the selector returned by DosAllocHuge as the first selector). For example:

  • Assume DosAllocHuge is issued with NumSeg equal to 3, and that the number 63 is returned for the selector of the first segment.
  • If DosGetHugeShift returns a shift count of 4, shifting the value “1” by this amount results in an increment of 16.
  • Adding this increment to selector number 63 produces 79 for the second selector. Adding the same increment to selector number 79 yields 95 for the third selector.

Example Code

C Binding

USHORT  rc = DosGetHugeShift(ShiftCount);
PUSHORT          ShiftCount;    /* Shift Count (returned) */
USHORT           rc;            /* return code */

MASM Binding

EXTRN  DosGetHugeShift:FAR
PUSH@  WORD    ShiftCount    ;Shift Count (returned)
CALL   DosGetHugeShift
Returns WORD