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updated.
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icculus committed Oct 1, 2000
1 parent 06684e3 commit 954d9bf
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2 changes: 2 additions & 0 deletions docs/contributors.txt
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@@ -1,2 +1,4 @@
Project founders: Ryan C. Gordon and Gregory S. Read.

Hopefully more to come...

138 changes: 71 additions & 67 deletions docs/randomizing_lab_notes.txt
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Expand Up @@ -163,11 +163,12 @@ generated code optimizations. Just wanted to point that out.

Anyhow, the code:

;
; RND with no arguments is identical to RND(1) (or any value > 0).
; In fact, it calls right into the middle of the RND-with-argument
; version of the function.
;
;
; RND with no arguments is identical to RND(1) (or any value > 0).
; In fact, it calls right into the middle of the RND-with-argument
; version of the function.
;

B$RND0: ; RND with NO arguments.
3563:0000 55 PUSH BP ; Save base pointer.
3563:0001 8BEC MOV BP,SP ; setup new base.
Expand All @@ -176,25 +177,25 @@ B$RND0: ; RND with NO arguments.
3563:0007 CB RETF ; return far.


;
; Qbasic help file on RND tells this about param's value:
; Less than 0 The same number for any n#
; Greater than 0 (or omitted) The next random number
; 0 The last number generated
;
; The stack after frame setup: bp+8 1/2 of parameter (SINGLE).
; bp+6 1/2 of parameter (SINGLE).
; bp+4 return address segment.
; bp+2 return address offset.
; bp+0 prev base pointer
;
; Qbasic help file on RND tells this about param's value:
; Less than 0 The same number for any n#
; Greater than 0 (or omitted) The next random number
; 0 The last number generated
;
; The stack after frame setup: bp+8 1/2 of parameter (SINGLE).
; bp+6 1/2 of parameter (SINGLE).
; bp+4 return address segment.
; bp+2 return address offset.
; bp+0 prev base pointer

B$RND1: ; RND with integer argument (the other RND just calls into here...)
3563:0008 55 PUSH BP ; Save base pointer.
3563:0009 8BEC MOV BP,SP ; setup new base.
3563:000B 8B4608 MOV AX,WORD PTR [BP+08] ; put param into AX.
3563:000E 0BC0 OR AX,AX ; is it 0?
3563:0010 741A JZ rndLastGen ; yes? goto rndlastGen.
3563:0012 7913 JNS rndNextGen ; if > 0, get next num.
3563:0012 7913 JNS rndNextGen ; if !neg, get next num.

; if here, param is < 0.
3563:0014 8B5606 MOV DX,WORD PTR [BP+06] ; other half of arg->dx.
Expand Down Expand Up @@ -314,8 +315,8 @@ rndNextEntry: ; Entry to next number in sequence generation algorithm...
; integer format, once this is on the coprocessor stack, it
; actually is 16777216.0 (or 0x1000000; it might as well be
; an integer, but the coprocessor is probably faster and easier
; to code. This calculation is to make sure the next number in
; the sequence is always between 0.0 and 1.0.
; to code. This calculation is probably to make sure the next number
; in the sequence is always between 0.0 and 1.0.
;
; Remember that functions returning a floating point number return the
; address in memory where you can find the real retval. 0x144
Expand All @@ -336,40 +337,42 @@ rndLastEntry: ; Entry to last number in sequence generation algorithm...
3563:0078 C3 RET


;
; Qbasic help file on RANDOMIZE tells this about param's value:
;
; Any type of numeric expression; used to initialize the
; random-number generator; if omitted, the value of the
; TIMER function is used.
;
; Where the comment is "stick in seed." below, the random seed is only
; partially overwritten. We stick 16 new bits into the middle of a block
; of 32.
;
; What happens is this: The argument is 8 bytes long, and we don't care that
; it's a DOUBLE so much as it is a collection of 64 bits. The bottom half of
; the parameter is thrown away, and the third word (16 bits) is XOR'd with
; the fourth. The new word produced by this XOR operation is then placed into
; the seed variable, at a one byte offset, which gives us a completely new
; set of bits, and is more or less suitable for reseeding the random number
; generator. The new seed then can be viewed as a SINGLE number again,
; instead of as a collection of 32 bits.
;
; Note that since we leave the first and last bytes of the seed "as-is", this
; function is not suitable for a complete resetting of the random number
; sequence. You need to use RND(x) where x < 0, or restart your program to
; get a consistent sequence from a value passed to this function. Yuck.
;
; The stack after frame setup: bp+0C 1/4 of parameter (DOUBLE).
; bp+0A 1/4 of parameter (DOUBLE).
; bp+08 1/4 of parameter (DOUBLE).
; bp+06 1/4 of parameter (DOUBLE).
; bp+04 return address segment.
; bp+02 return address offset.
; bp+00 prev base pointer
;

;
; Qbasic help file on RANDOMIZE tells this about param's value:
;
; Any type of numeric expression; used to initialize the
; random-number generator; if omitted, the value of the
; TIMER function is used.
;
; Where the comment is "stick in seed." below, the random seed is only
; partially overwritten. We stick 16 new bits into the middle of a
; block of 32.
;
; What happens is this: The argument is 8 bytes long, and we don't
; care that it's a DOUBLE so much as it is a collection of 64 bits.
; The bottom half of the parameter is thrown away, and the third word
; (16 bits) is XOR'd with the fourth. The new word produced by this
; XOR operation is then placed into the seed variable, at a one byte
; offset, which gives us a completely new set of bits, and is more or
; less suitable for reseeding the random number generator. The new
; seed then can be viewed as a SINGLE number again, instead of as a
; collection of 32 bits.
;
; Note that since we leave the first and last bytes of the seed
; "as-is", this function is not suitable for a complete resetting of
; the random number sequence. You need to use RND(x) where x < 0, or
; restart your program to get a consistent sequence from a value
; passed to this function. Yuck.
;
; The stack after frame setup: bp+0C 1/4 of parameter (DOUBLE).
; bp+0A 1/4 of parameter (DOUBLE).
; bp+08 1/4 of parameter (DOUBLE).
; bp+06 1/4 of parameter (DOUBLE).
; bp+04 return address segment.
; bp+02 return address offset.
; bp+00 prev base pointer
;

B$RNZP: ; RANDOMIZE with specific seed.
3563:0079 55 PUSH BP ; Save base ptr.
3563:007A 8BEC MOV BP,SP ; Set new base.
Expand All @@ -381,19 +384,20 @@ B$RNZP: ; RANDOMIZE with specific seed.
3563:0088 CA0800 RETF 0008 ; Return far.


;
; RANDOMIZE without an argument is more or less just shorthand for
; RANDOMIZE TIMER, and makes your code a few opcodes smaller, since it does
; the work inside the runtime library. So the code below does just that;
; CALLs B$TIMR (BASIC's TIMER function, not the statement version), takes the
; retval, and gives it the same XOR treatment as above. Note that TIMER
; returns a SINGLE, even though RANDOMIZE-with-an-argument needs a DOUBLE.
; This would explain why four bytes of the argument you pass to RANDOMIZE are
; thrown away; for compatibility with this (and probably legacy BASIC) code.
;
; The stack after frame setup: bp+02 return address segment.
; (there is no setup, really.) bp+00 return address offset.
;
;
; RANDOMIZE without an argument is more or less just shorthand for
; RANDOMIZE TIMER, and makes your code a few opcodes smaller, since
; it does the work inside the runtime library. So the code below
; does just that; CALLs B$TIMR (BASIC's TIMER function, not the
; statement version), takes the retval, and gives it the same XOR
; treatment as above. Note that TIMER returns a SINGLE, even though
; RANDOMIZE-with-an-argument needs a DOUBLE. This would explain why
; four bytes of the argument you pass to RANDOMIZE are thrown away;
; for compatibility with this (and probably legacy BASIC) code.
;
; The stack after frame setup: bp+02 return address segment.
; (there is no setup, really.) bp+00 return address offset.
;

B$RNZ0: ; RANDOMIZE without specific seed.
3563:008B 9AD0066335 CALL B$TIMR ; Call TIMER().
Expand Down Expand Up @@ -603,7 +607,7 @@ __single _vbf_timer(void); /* need this for _vbp_randomize() .. */
/* These are the (hopefully) constants in b$EightSpaces... */
#define ENTROPY1 0x43FD // -000C
#define ENTROPY2 0x9EC3 // -0008
#define ENTROPY3 0x195 // just first char of -0008.
#define ENTROPY3 0xC3 // just first char of -0008.
#define ENTROPY4 (__single) 0x1000000 // -0004 (dword)

/* The psuedorandom seed. */
Expand Down

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