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math/big: remove the s390x assembly for shlVU and shrVU
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The s390x assembly for shlVU does a forward copy when the shift amount s
is 0. This causes corruption of the result z when z is aliased to the
input x.

This fix removes the s390x assembly for both shlVU and shrVU so the pure
go implementations will be used.

Test cases have been added to the existing TestShiftOverlap test to
cover shift values of 0, 1 and (_W - 1).

Fixes #42838

Change-Id: I75ca0e98f3acfaa6366a26355dcd9dd82499a48b
Reviewed-on: https://go-review.googlesource.com/c/go/+/274442
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
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@jonathan-albrecht-ibm @mdempsky
jonathan-albrecht-ibm authored and mdempsky committed Dec 3, 2020
1 parent dda2991 commit b1369d5
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192 changes: 2 additions & 190 deletions src/math/big/arith_s390x.s
View file
Original file line number Diff line number Diff line change
Expand Up @@ -693,199 +693,11 @@ returnC:

// func shlVU(z, x []Word, s uint) (c Word)
TEXT ·shlVU(SB), NOSPLIT, $0
MOVD z_len+8(FP), R5
MOVD $0, R0
SUB $1, R5 // n--
BLT X8b // n < 0 (n <= 0)

// n > 0
MOVD s+48(FP), R4
CMPBEQ R0, R4, Z80 // handle 0 case beq
MOVD $64, R6
CMPBEQ R6, R4, Z864 // handle 64 case beq
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8
SUB R4, R6, R7
MOVD (R8)(R5*1), R10 // w1 = x[i-1]
SRD R7, R10, R3
MOVD R3, c+56(FP)

MOVD $0, R1 // i = 0
BR E8

// i < n-1
L8:
MOVD R10, R3 // w = w1
MOVD -8(R8)(R5*1), R10 // w1 = x[i+1]

SLD R4, R3 // w<<s | w1>>ŝ
SRD R7, R10, R6
OR R6, R3
MOVD R3, (R2)(R5*1) // z[i] = w<<s | w1>>ŝ
SUB $8, R5 // i--

E8:
CMPBGT R5, R0, L8 // i < n-1

// i >= n-1
X8a:
SLD R4, R10 // w1<<s
MOVD R10, (R2) // z[0] = w1<<s
RET

X8b:
MOVD R0, c+56(FP)
RET

Z80:
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8

MOVD (R8), R10
MOVD $0, R3
MOVD R3, c+56(FP)

MOVD $0, R1 // i = 0
BR E8Z

// i < n-1
L8Z:
MOVD R10, R3
MOVD 8(R8)(R1*1), R10

MOVD R3, (R2)(R1*1)
ADD $8, R1

E8Z:
CMPBLT R1, R5, L8Z

// i >= n-1
MOVD R10, (R2)(R5*1)
RET

Z864:
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8
MOVD (R8)(R5*1), R3 // w1 = x[n-1]
MOVD R3, c+56(FP) // z[i] = x[n-1]

BR E864

// i < n-1
L864:
MOVD -8(R8)(R5*1), R3

MOVD R3, (R2)(R5*1) // z[i] = x[n-1]
SUB $8, R5 // i--

E864:
CMPBGT R5, R0, L864 // i < n-1

MOVD R0, (R2) // z[n-1] = 0
RET
BR ·shlVU_g(SB)

// CX = R4, r8 = r8, r10 = r2 , r11 = r5, DX = r3, AX = r10 , BX = R1 , 64-count = r7 (R0 set to 0) temp = R6
// func shrVU(z, x []Word, s uint) (c Word)
TEXT ·shrVU(SB), NOSPLIT, $0
MOVD z_len+8(FP), R5
MOVD $0, R0
SUB $1, R5 // n--
BLT X9b // n < 0 (n <= 0)

// n > 0
MOVD s+48(FP), R4
CMPBEQ R0, R4, ZB0 // handle 0 case beq
MOVD $64, R6
CMPBEQ R6, R4, ZB64 // handle 64 case beq
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8
SUB R4, R6, R7
MOVD (R8), R10 // w1 = x[0]
SLD R7, R10, R3
MOVD R3, c+56(FP)

MOVD $0, R1 // i = 0
BR E9

// i < n-1
L9:
MOVD R10, R3 // w = w1
MOVD 8(R8)(R1*1), R10 // w1 = x[i+1]

SRD R4, R3 // w>>s | w1<<s
SLD R7, R10, R6
OR R6, R3
MOVD R3, (R2)(R1*1) // z[i] = w>>s | w1<<s
ADD $8, R1 // i++

E9:
CMPBLT R1, R5, L9 // i < n-1

// i >= n-1
X9a:
SRD R4, R10 // w1>>s
MOVD R10, (R2)(R5*1) // z[n-1] = w1>>s
RET

X9b:
MOVD R0, c+56(FP)
RET

ZB0:
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8

MOVD (R8), R10 // w1 = x[0]
MOVD $0, R3 // R10 << 64
MOVD R3, c+56(FP)

MOVD $0, R1 // i = 0
BR E9Z

// i < n-1
L9Z:
MOVD R10, R3 // w = w1
MOVD 8(R8)(R1*1), R10 // w1 = x[i+1]

MOVD R3, (R2)(R1*1) // z[i] = w>>s | w1<<s
ADD $8, R1 // i++

E9Z:
CMPBLT R1, R5, L9Z // i < n-1

// i >= n-1
MOVD R10, (R2)(R5*1) // z[n-1] = w1>>s
RET

ZB64:
MOVD z+0(FP), R2
MOVD x+24(FP), R8
SLD $3, R5 // n = n*8
MOVD (R8), R3 // w1 = x[0]
MOVD R3, c+56(FP)

MOVD $0, R1 // i = 0
BR E964

// i < n-1
L964:
MOVD 8(R8)(R1*1), R3 // w1 = x[i+1]

MOVD R3, (R2)(R1*1) // z[i] = w>>s | w1<<s
ADD $8, R1 // i++

E964:
CMPBLT R1, R5, L964 // i < n-1

// i >= n-1
MOVD $0, R10 // w1>>s
MOVD R10, (R2)(R5*1) // z[n-1] = w1>>s
RET
BR ·shrVU_g(SB)

// CX = R4, r8 = r8, r9=r9, r10 = r2 , r11 = r5, DX = r3, AX = r6 , BX = R1 , (R0 set to 0) + use R11 + use R7 for i
// func mulAddVWW(z, x []Word, y, r Word) (c Word)
Expand Down
55 changes: 52 additions & 3 deletions src/math/big/arith_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -285,20 +285,56 @@ type argVU struct {
m string // message.
}

var argshlVUIn = []Word{1, 2, 4, 8, 16, 32, 64, 0, 0, 0}
var argshlVUr0 = []Word{1, 2, 4, 8, 16, 32, 64}
var argshlVUr1 = []Word{2, 4, 8, 16, 32, 64, 128}
var argshlVUrWm1 = []Word{1 << (_W - 1), 0, 1, 2, 4, 8, 16}

var argshlVU = []argVU{
// test cases for shlVU
{[]Word{1, _M, _M, _M, _M, _M, 3 << (_W - 2), 0}, 7, 0, 0, 1, []Word{2, _M - 1, _M, _M, _M, _M, 1<<(_W-1) + 1}, 1, "complete overlap of shlVU"},
{[]Word{1, _M, _M, _M, _M, _M, 3 << (_W - 2), 0, 0, 0, 0}, 7, 0, 3, 1, []Word{2, _M - 1, _M, _M, _M, _M, 1<<(_W-1) + 1}, 1, "partial overlap by half of shlVU"},
{[]Word{1, _M, _M, _M, _M, _M, 3 << (_W - 2), 0, 0, 0, 0, 0, 0, 0}, 7, 0, 6, 1, []Word{2, _M - 1, _M, _M, _M, _M, 1<<(_W-1) + 1}, 1, "partial overlap by 1 Word of shlVU"},
{[]Word{1, _M, _M, _M, _M, _M, 3 << (_W - 2), 0, 0, 0, 0, 0, 0, 0, 0}, 7, 0, 7, 1, []Word{2, _M - 1, _M, _M, _M, _M, 1<<(_W-1) + 1}, 1, "no overlap of shlVU"},
}
// additional test cases with shift values of 0, 1 and (_W-1)
{argshlVUIn, 7, 0, 0, 0, argshlVUr0, 0, "complete overlap of shlVU and shift of 0"},
{argshlVUIn, 7, 0, 0, 1, argshlVUr1, 0, "complete overlap of shlVU and shift of 1"},
{argshlVUIn, 7, 0, 0, _W - 1, argshlVUrWm1, 32, "complete overlap of shlVU and shift of _W - 1"},
{argshlVUIn, 7, 0, 1, 0, argshlVUr0, 0, "partial overlap by 6 Words of shlVU and shift of 0"},
{argshlVUIn, 7, 0, 1, 1, argshlVUr1, 0, "partial overlap by 6 Words of shlVU and shift of 1"},
{argshlVUIn, 7, 0, 1, _W - 1, argshlVUrWm1, 32, "partial overlap by 6 Words of shlVU and shift of _W - 1"},
{argshlVUIn, 7, 0, 2, 0, argshlVUr0, 0, "partial overlap by 5 Words of shlVU and shift of 0"},
{argshlVUIn, 7, 0, 2, 1, argshlVUr1, 0, "partial overlap by 5 Words of shlVU and shift of 1"},
{argshlVUIn, 7, 0, 2, _W - 1, argshlVUrWm1, 32, "partial overlap by 5 Words of shlVU abd shift of _W - 1"},
{argshlVUIn, 7, 0, 3, 0, argshlVUr0, 0, "partial overlap by 4 Words of shlVU and shift of 0"},
{argshlVUIn, 7, 0, 3, 1, argshlVUr1, 0, "partial overlap by 4 Words of shlVU and shift of 1"},
{argshlVUIn, 7, 0, 3, _W - 1, argshlVUrWm1, 32, "partial overlap by 4 Words of shlVU and shift of _W - 1"},
}

var argshrVUIn = []Word{0, 0, 0, 1, 2, 4, 8, 16, 32, 64}
var argshrVUr0 = []Word{1, 2, 4, 8, 16, 32, 64}
var argshrVUr1 = []Word{0, 1, 2, 4, 8, 16, 32}
var argshrVUrWm1 = []Word{4, 8, 16, 32, 64, 128, 0}

var argshrVU = []argVU{
// test cases for shrVU
{[]Word{0, 3, _M, _M, _M, _M, _M, 1 << (_W - 1)}, 7, 1, 1, 1, []Word{1<<(_W-1) + 1, _M, _M, _M, _M, _M >> 1, 1 << (_W - 2)}, 1 << (_W - 1), "complete overlap of shrVU"},
{[]Word{0, 0, 0, 0, 3, _M, _M, _M, _M, _M, 1 << (_W - 1)}, 7, 4, 1, 1, []Word{1<<(_W-1) + 1, _M, _M, _M, _M, _M >> 1, 1 << (_W - 2)}, 1 << (_W - 1), "partial overlap by half of shrVU"},
{[]Word{0, 0, 0, 0, 0, 0, 0, 3, _M, _M, _M, _M, _M, 1 << (_W - 1)}, 7, 7, 1, 1, []Word{1<<(_W-1) + 1, _M, _M, _M, _M, _M >> 1, 1 << (_W - 2)}, 1 << (_W - 1), "partial overlap by 1 Word of shrVU"},
{[]Word{0, 0, 0, 0, 0, 0, 0, 0, 3, _M, _M, _M, _M, _M, 1 << (_W - 1)}, 7, 8, 1, 1, []Word{1<<(_W-1) + 1, _M, _M, _M, _M, _M >> 1, 1 << (_W - 2)}, 1 << (_W - 1), "no overlap of shrVU"},
// additional test cases with shift values of 0, 1 and (_W-1)
{argshrVUIn, 7, 3, 3, 0, argshrVUr0, 0, "complete overlap of shrVU and shift of 0"},
{argshrVUIn, 7, 3, 3, 1, argshrVUr1, 1 << (_W - 1), "complete overlap of shrVU and shift of 1"},
{argshrVUIn, 7, 3, 3, _W - 1, argshrVUrWm1, 2, "complete overlap of shrVU and shift of _W - 1"},
{argshrVUIn, 7, 3, 2, 0, argshrVUr0, 0, "partial overlap by 6 Words of shrVU and shift of 0"},
{argshrVUIn, 7, 3, 2, 1, argshrVUr1, 1 << (_W - 1), "partial overlap by 6 Words of shrVU and shift of 1"},
{argshrVUIn, 7, 3, 2, _W - 1, argshrVUrWm1, 2, "partial overlap by 6 Words of shrVU and shift of _W - 1"},
{argshrVUIn, 7, 3, 1, 0, argshrVUr0, 0, "partial overlap by 5 Words of shrVU and shift of 0"},
{argshrVUIn, 7, 3, 1, 1, argshrVUr1, 1 << (_W - 1), "partial overlap by 5 Words of shrVU and shift of 1"},
{argshrVUIn, 7, 3, 1, _W - 1, argshrVUrWm1, 2, "partial overlap by 5 Words of shrVU and shift of _W - 1"},
{argshrVUIn, 7, 3, 0, 0, argshrVUr0, 0, "partial overlap by 4 Words of shrVU and shift of 0"},
{argshrVUIn, 7, 3, 0, 1, argshrVUr1, 1 << (_W - 1), "partial overlap by 4 Words of shrVU and shift of 1"},
{argshrVUIn, 7, 3, 0, _W - 1, argshrVUrWm1, 2, "partial overlap by 4 Words of shrVU and shift of _W - 1"},
}

func testShiftFunc(t *testing.T, f func(z, x []Word, s uint) Word, a argVU) {
Expand Down Expand Up @@ -335,11 +371,24 @@ func TestIssue31084(t *testing.T) {
// compute 10^n via 5^n << n.
const n = 165
p := nat(nil).expNN(nat{5}, nat{n}, nil)
p = p.shl(p, uint(n))
p = p.shl(p, n)
got := string(p.utoa(10))
want := "1" + strings.Repeat("0", n)
if got != want {
t.Errorf("shl(%v, %v)\n\tgot %s; want %s\n", p, uint(n), got, want)
t.Errorf("shl(%v, %v)\n\tgot %s\n\twant %s", p, n, got, want)
}
}

const issue42838Value = "159309191113245227702888039776771180559110455519261878607388585338616290151305816094308987472018268594098344692611135542392730712890625"

func TestIssue42838(t *testing.T) {
const s = 192
z, _, _, _ := nat(nil).scan(strings.NewReader(issue42838Value), 0, false)
z = z.shl(z, s)
got := string(z.utoa(10))
want := "1" + strings.Repeat("0", s)
if got != want {
t.Errorf("shl(%v, %v)\n\tgot %s\n\twant %s", z, s, got, want)
}
}

Expand Down

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