MOVW R7, 4(R(arg))
RET
-
-Q = 0
-N = 1
-D = 2
-CC = 3
-TMP = 11
-
-TEXT save<>(SB), 7, $0
- MOVW R(Q), 0(FP)
- MOVW R(N), 4(FP)
- MOVW R(D), 8(FP)
- MOVW R(CC), 12(FP)
-
- MOVW R(TMP), R(Q) /* numerator */
- MOVW 20(FP), R(D) /* denominator */
- CMP $0, R(D)
- BNE s1
- BL runtime·panicdivide(SB)
-/* MOVW -1(R(D)), R(TMP) /* divide by zero fault */
-s1: RET
-
-TEXT rest<>(SB), 7, $0
- MOVW 0(FP), R(Q)
- MOVW 4(FP), R(N)
- MOVW 8(FP), R(D)
- MOVW 12(FP), R(CC)
-/*
- * return to caller
- * of rest<>
- */
- MOVW 0(R13), R14
- ADD $20, R13
- B (R14)
-
-TEXT div<>(SB), 7, $0
- MOVW $32, R(CC)
-/*
- * skip zeros 8-at-a-time
- */
-e1:
- AND.S $(0xff<<24),R(Q), R(N)
- BNE e2
- SLL $8, R(Q)
- SUB.S $8, R(CC)
- BNE e1
- RET
-e2:
- MOVW $0, R(N)
-
-loop:
-/*
- * shift R(N||Q) left one
- */
- SLL $1, R(N)
- CMP $0, R(Q)
- ORR.LT $1, R(N)
- SLL $1, R(Q)
-
-/*
- * compare numerator to denominator
- * if less, subtract and set quotient bit
- */
- CMP R(D), R(N)
- ORR.HS $1, R(Q)
- SUB.HS R(D), R(N)
- SUB.S $1, R(CC)
- BNE loop
- RET
-
-TEXT _div(SB), 7, $16
- BL save<>(SB)
- CMP $0, R(Q)
- BGE d1
- RSB $0, R(Q), R(Q)
- CMP $0, R(D)
- BGE d2
- RSB $0, R(D), R(D)
-d0:
- BL div<>(SB) /* none/both neg */
- MOVW R(Q), R(TMP)
- B out
-d1:
- CMP $0, R(D)
- BGE d0
- RSB $0, R(D), R(D)
-d2:
- BL div<>(SB) /* one neg */
- RSB $0, R(Q), R(TMP)
- B out
-
-TEXT _mod(SB), 7, $16
- BL save<>(SB)
- CMP $0, R(D)
- RSB.LT $0, R(D), R(D)
- CMP $0, R(Q)
- BGE m1
- RSB $0, R(Q), R(Q)
- BL div<>(SB) /* neg numerator */
- RSB $0, R(N), R(TMP)
- B out
-m1:
- BL div<>(SB) /* pos numerator */
- MOVW R(N), R(TMP)
- B out
-
-TEXT _divu(SB), 7, $16
- BL save<>(SB)
- BL div<>(SB)
- MOVW R(Q), R(TMP)
- B out
-
-TEXT _modu(SB), 7, $16
- BL save<>(SB)
- BL div<>(SB)
- MOVW R(N), R(TMP)
- B out
-
-out:
- BL rest<>(SB)
- B out
-
// trampoline for _sfloat2. passes LR as arg0 and
// saves registers R0-R13 and CPSR on the stack. R0-R12 and CPSR flags can
// be changed by _sfloat2.
MOVM.IA.W (R0), [R1-R12]
MOVW 8(R13), R0
RET
-
+// func udiv(n, d uint32) (q, r uint32)
+// Reference:
+// Sloss, Andrew et. al; ARM System Developer's Guide: Designing and Optimizing System Software
+// Morgan Kaufmann; 1 edition (April 8, 2004), ISBN 978-1558608740
+q = 0 // input d, output q
+r = 1 // input n, output r
+s = 2 // three temporary variables
+m = 3
+a = 11
+// Please be careful when changing this, it is pretty fragile:
+// 1, don't use unconditional branch as the linker is free to reorder the blocks;
+// 2. if a == 11, beware that the linker will use R11 if you use certain instructions.
+TEXT udiv<>(SB),7,$-4
+ CLZ R(q), R(s) // find normalizing shift
+ MOVW.S R(q)<<R(s), R(a)
+ ADD R(a)>>25, PC, R(a) // most significant 7 bits of divisor
+ MOVBU.NE (4*36-64)(R(a)), R(a) // 36 == number of inst. between fast_udiv_tab and begin
+
+begin:
+ SUB.S $7, R(s)
+ RSB $0, R(q), R(m) // m = -q
+ MOVW.PL R(a)<<R(s), R(q)
+
+ // 1st Newton iteration
+ MUL.PL R(m), R(q), R(a) // a = -q*d
+ BMI udiv_by_large_d
+ MULAWT R(a), R(q), R(q), R(q) // q approx q-(q*q*d>>32)
+ TEQ R(m)->1, R(m) // check for d=0 or d=1
+
+ // 2nd Newton iteration
+ MUL.NE R(m), R(q), R(a)
+ MOVW.NE $0, R(s)
+ MULAL.NE R(q), R(a), (R(q),R(s))
+ BEQ udiv_by_0_or_1
+
+ // q now accurate enough for a remainder r, 0<=r<3*d
+ MULLU R(q), R(r), (R(q),R(s)) // q = (r * q) >> 32
+ ADD R(m), R(r), R(r) // r = n - d
+ MULA R(m), R(q), R(r), R(r) // r = n - (q+1)*d
+
+ // since 0 <= n-q*d < 3*d; thus -d <= r < 2*d
+ CMN R(m), R(r) // t = r-d
+ SUB.CS R(m), R(r), R(r) // if (t<-d || t>=0) r=r+d
+ ADD.CC $1, R(q)
+ ADD.PL R(m)<<1, R(r)
+ ADD.PL $2, R(q)
+
+ // return, can't use RET here or fast_udiv_tab will be dropped during linking
+ MOVW R14, R15
+
+udiv_by_large_d:
+ // at this point we know d>=2^(31-6)=2^25
+ SUB $4, R(a), R(a)
+ RSB $0, R(s), R(s)
+ MOVW R(a)>>R(s), R(q)
+ MULLU R(q), R(r), (R(q),R(s))
+ MULA R(m), R(q), R(r), R(r)
+
+ // q now accurate enough for a remainder r, 0<=r<4*d
+ CMN R(r)>>1, R(m) // if(r/2 >= d)
+ ADD.CS R(m)<<1, R(r)
+ ADD.CS $2, R(q)
+ CMN R(r), R(m)
+ ADD.CS R(m), R(r)
+ ADD.CS $1, R(q)
+
+ // return, can't use RET here or fast_udiv_tab will be dropped during linking
+ MOVW R14, R15
+
+udiv_by_0_or_1:
+ // carry set if d==1, carry clear if d==0
+ MOVW.CS R(r), R(q)
+ MOVW.CS $0, R(r)
+ BL.CC runtime·panicdivide(SB) // no way back
+
+ // return, can't use RET here or fast_udiv_tab will be dropped during linking
+ MOVW R14, R15
+
+fast_udiv_tab:
+ // var tab [64]byte
+ // tab[0] = 255; for i := 1; i <= 63; i++ { tab[i] = (1<<14)/(64+i) }
+ // laid out here as little-endian uint32s
+ WORD $0xf4f8fcff
+ WORD $0xe6eaedf0
+ WORD $0xdadde0e3
+ WORD $0xcfd2d4d7
+ WORD $0xc5c7cacc
+ WORD $0xbcbec0c3
+ WORD $0xb4b6b8ba
+ WORD $0xacaeb0b2
+ WORD $0xa5a7a8aa
+ WORD $0x9fa0a2a3
+ WORD $0x999a9c9d
+ WORD $0x93949697
+ WORD $0x8e8f9092
+ WORD $0x898a8c8d
+ WORD $0x85868788
+ WORD $0x81828384
+
+// The linker will pass numerator in R(TMP), and it also
+// expects the result in R(TMP)
+TMP = 11
+
+TEXT _divu(SB), 7, $16
+ MOVW R(q), 4(R13)
+ MOVW R(r), 8(R13)
+ MOVW R(s), 12(R13)
+ MOVW R(m), 16(R13)
+
+ MOVW R(TMP), R(r) /* numerator */
+ MOVW 0(FP), R(q) /* denominator */
+ BL udiv<>(SB)
+ MOVW R(q), R(TMP)
+ MOVW 4(R13), R(q)
+ MOVW 8(R13), R(r)
+ MOVW 12(R13), R(s)
+ MOVW 16(R13), R(m)
+ RET
+
+TEXT _modu(SB), 7, $16
+ MOVW R(q), 4(R13)
+ MOVW R(r), 8(R13)
+ MOVW R(s), 12(R13)
+ MOVW R(m), 16(R13)
+
+ MOVW R(TMP), R(r) /* numerator */
+ MOVW 0(FP), R(q) /* denominator */
+ BL udiv<>(SB)
+ MOVW R(r), R(TMP)
+ MOVW 4(R13), R(q)
+ MOVW 8(R13), R(r)
+ MOVW 12(R13), R(s)
+ MOVW 16(R13), R(m)
+ RET
+
+TEXT _div(SB),7,$16
+ MOVW R(q), 4(R13)
+ MOVW R(r), 8(R13)
+ MOVW R(s), 12(R13)
+ MOVW R(m), 16(R13)
+ MOVW R(TMP), R(r) /* numerator */
+ MOVW 0(FP), R(q) /* denominator */
+ CMP $0, R(r)
+ BGE d1
+ RSB $0, R(r), R(r)
+ CMP $0, R(q)
+ BGE d2
+ RSB $0, R(q), R(q)
+d0:
+ BL udiv<>(SB) /* none/both neg */
+ MOVW R(q), R(TMP)
+ B out
+d1:
+ CMP $0, R(q)
+ BGE d0
+ RSB $0, R(q), R(q)
+d2:
+ BL udiv<>(SB) /* one neg */
+ RSB $0, R(q), R(TMP)
+ B out
+
+TEXT _mod(SB),7,$16
+ MOVW R(q), 4(R13)
+ MOVW R(r), 8(R13)
+ MOVW R(s), 12(R13)
+ MOVW R(m), 16(R13)
+ MOVW R(TMP), R(r) /* numerator */
+ MOVW 0(FP), R(q) /* denominator */
+ CMP $0, R(q)
+ RSB.LT $0, R(q), R(q)
+ CMP $0, R(r)
+ BGE m1
+ RSB $0, R(r), R(r)
+ BL udiv<>(SB) /* neg numerator */
+ RSB $0, R(r), R(TMP)
+ B out
+m1:
+ BL udiv<>(SB) /* pos numerator */
+ MOVW R(r), R(TMP)
+out:
+ MOVW 4(R13), R(q)
+ MOVW 8(R13), R(r)
+ MOVW 12(R13), R(s)
+ MOVW 16(R13), R(m)
+ RET