788cceaab9
Deleted several unused modules and some commented code Reorganized some routines to clean up modules Moved some memory into mirrored WRAM Refactored NMI hook aux routine Removed old fake flipper fix
211 lines
5.3 KiB
NASM
211 lines
5.3 KiB
NASM
; Scrap04 used for n
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; Scrap06 used for rounds
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; Scrap08 use for dpScratch/MXResult (lower 32 of dpScratch)
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CryptoDelta:
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dd #$9e3779b9
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; For use in an unrolled loop
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macro LSR32Single(value)
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CLC;
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LDA.b <value>+2 : ROR : STA.b <value>+2 ; do top part
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LDA.b <value> : ROR : STA.b <value> ; do bottom part
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; ROR handles the carry from the upper byte for us
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endmacro
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macro ASL32Single(value)
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CLC
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LDA.b <value> : ROL : STA.b <value> ; do bottom part
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LDA.b <value>+2 : ROL : STA.b <value>+2 ; do top part
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; ROL handles the carry from the lower byte for us
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endmacro
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CryptoMX:
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PHX
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; upperScratch = (z>>5 ^ y <<2)
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LDA.w z : STA.b Scrap08
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LDA.w z+2 : STA.b Scrap08+2
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%LSR32Single(Scrap08)
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%LSR32Single(Scrap08)
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%LSR32Single(Scrap08)
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%LSR32Single(Scrap08)
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%LSR32Single(Scrap08)
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;%LSR32(Scrap08,#$05)
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LDA.w y : STA.b Scrap08+4
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LDA.w y+2 : STA.b Scrap08+6
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%ASL32Single(Scrap08+4)
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%ASL32Single(Scrap08+4)
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;%ASL32(Scrap08+4,#$02)
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LDA.b Scrap08 : EOR.b Scrap08+4 : STA.w CryptoScratch
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LDA.b Scrap08+2 : EOR.b Scrap08+6 : STA.w CryptoScratch+2
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;================================
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; upperscratch2 = (y>>3^z<<4)
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LDA.w z : STA.b Scrap08
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LDA.w z+2 : STA.b Scrap08+2
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%ASL32Single(Scrap08)
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%ASL32Single(Scrap08)
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%ASL32Single(Scrap08)
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%ASL32Single(Scrap08)
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;%ASL32(Scrap08,#$04)
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LDA.w y : STA.b Scrap08+4
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LDA.w y+2 : STA.b Scrap08+6
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%LSR32Single(Scrap08+4)
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%LSR32Single(Scrap08+4)
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%LSR32Single(Scrap08+4)
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;%LSR32(Scrap08+4,#$03)
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LDA.b Scrap08 : EOR.b Scrap08+4 : STA.w CryptoScratch+4
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LDA.b Scrap08+2 : EOR.b Scrap08+6 : STA.w CryptoScratch+6
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;================================
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; upperscratch = upperscratch + upperscratch2 ( == (z>>5^y<<2) + (y>>3^z<<4) )
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LDA.w CryptoScratch : !ADD.w CryptoScratch+4 : STA.w CryptoScratch
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LDA.w CryptoScratch+2 : ADC.w CryptoScratch+6 : STA.w CryptoScratch+2
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;================================
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; dpscratch = sum^y
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LDA.w Sum : EOR.w y : STA.b Scrap08
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LDA.w Sum+2 : EOR.w y+2 : STA.b Scrap08+2
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;================================
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; dpscratch2 = (k[p&3^e]^z)
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LDA.w p : AND.w #$0003 : EOR.w e : ASL #2 : TAX ; put (p&3)^e into X
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LDA.w KeyBase, X : EOR.w z : STA.b Scrap08+4
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LDA.w KeyBase+2, X : EOR.w z+2 : STA.b Scrap08+6
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;================================
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; upperscratch2 = dpscratch + dpscratch2 (== (sum^y) + (k[p&3^e]^z))
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LDA.b Scrap08 : !ADD.b Scrap08+4 : STA.w CryptoScratch+4
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LDA.b Scrap08+2 : ADC.b Scrap08+6 : STA.w CryptoScratch+6
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;================================
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; MXResult = uppserscratch ^ upperscratch2
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LDA.w CryptoScratch : EOR.w CryptoScratch+4 : STA.b Scrap08
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LDA.w CryptoScratch+2 : EOR.w CryptoScratch+6 : STA.b Scrap08+2
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PLX
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RTS
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XXTEA_Decode:
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PHP : PHB
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SEP #$30 ; set 8-bit accumulator and index
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LDA.b #$7F : PHA : PLB
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STZ.b Scrap04+1 ; set upper byte of n to be zero, so it can safely be accessed in 16-bit mode
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; search for lookup table index to avoid division and multiplication
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LDX.b #0
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-
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LDA.l .n_lookup, X
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CMP.b Scrap04 : !BLT +
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INX
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BRA -
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+
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; rounds = 6 + 52/n;
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LDA.l .round_counts, X : STA.b Scrap06 : STZ.b Scrap06+1
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REP #$20 ; set 16-bit accumulator
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; sum = rounds*DELTA;
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TXA : ASL #2 : TAX
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LDA.l .initial_sums, X : STA.w Sum
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LDA.l .initial_sums+2, X : STA.w Sum+2
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; y = v[0];
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LDA.w v : STA.w y
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LDA.w v+2 : STA.w y+2
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---
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LDA.w Sum : LSR #2 : AND.w #$0003 : STA.w e ; e = (sum >> 2) & 3;
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LDA.b Scrap04 : DEC : STA.w p
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-- BEQ + ; for (p=n-1; p>0; p--) {
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; z = v[p-1];
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ASL #2 : TAX
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LDA.w v-4, X : STA.w z
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LDA.w v-4+2, X : STA.w z+2
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; y = v[p] -= MX;
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JSR CryptoMX
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LDA.w p : ASL #2 : TAX
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LDA.w v, X : !SUB.b Scrap08 : STA.w v, X : STA.w y
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LDA.w v+2, X : SBC.b Scrap08+2 : STA.w v+2, X : STA.w y+2
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LDA.w p : DEC : STA.w p : BRA -- ; }
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+
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; z = v[n-1];
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LDA.b Scrap04 : DEC : ASL #2 : TAX
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LDA.w v, X : STA.w z
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LDA.w v+2, X : STA.w z+2
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; y = v[0] -= MX;
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JSR CryptoMX
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LDA.w v : !SUB.b Scrap08 : STA.w v : STA.w y
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LDA.w v+2 : SBC.b Scrap08+2 : STA.w v+2 : STA.w y+2
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; sum -= DELTA;
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LDA.w Sum : !SUB.l CryptoDelta : STA.w Sum
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LDA.w Sum+2 : SBC.l CryptoDelta+2 : STA.w Sum+2
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DEC.b Scrap06 : BEQ + : JMP --- : + ; } while (--rounds);
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PLB : PLP
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RTL
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; Note: uncomment any values from these tables that correspond to values of n actually in use
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; (unused values are commented out to improve performance/ avoid wasting space)
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.n_lookup
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;db 52 ; n > 52
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;db 26 ; n is 27 to 52
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;db 17 ; n is 18 to 26
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;db 13 ; n is 14 to 17
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;db 10 ; n is 11 to 13
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;db 8 ; n is 9 to 10
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;db 7 ; n is 8
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;db 6 ; n is 7
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;db 5 ; n is 6
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;db 4 ; n is 5
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;db 3 ; n is 4
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;db 2 ; n is 3
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db 1 ; n is 2
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.round_counts
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;db 6 ; n > 52
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;db 7 ; n is 27 to 52
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;db 8 ; n is 18 to 26
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;db 9 ; n is 14 to 17
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;db 10 ; n is 11 to 13
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;db 11 ; n is 9 to 10
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;db 12 ; n is 8
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;db 13 ; n is 7
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;db 14 ; n is 6
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;db 16 ; n is 5
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;db 19 ; n is 4
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;db 23 ; n is 3
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db 32 ; n is 2
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.initial_sums
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;dd (6*$9e3779b9)&$ffffffff ; n > 52
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;dd (7*$9e3779b9)&$ffffffff ; n is 27 to 52
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;dd (8*$9e3779b9)&$ffffffff ; n is 18 to 26
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;dd (9*$9e3779b9)&$ffffffff ; n is 14 to 17
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;dd (10*$9e3779b9)&$ffffffff ; n is 11 to 13
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;dd (11*$9e3779b9)&$ffffffff ; n is 9 to 10
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;dd (12*$9e3779b9)&$ffffffff ; n is 8
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;dd (13*$9e3779b9)&$ffffffff ; n is 7
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;dd (14*$9e3779b9)&$ffffffff ; n is 6
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;dd (16*$9e3779b9)&$ffffffff ; n is 5
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;dd (19*$9e3779b9)&$ffffffff ; n is 4
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;dd (23*$9e3779b9)&$ffffffff ; n is 3
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dd (32*$9e3779b9)&$ffffffff ; n is 2
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