GOOS=linux GOARCH=arm go run arm.go

package main

type decimal struct {
	d  [8]byte // digits, big-endian representation
	dp int     // decimal point
}

var powtab = []int{1, 3, 6, 9, 13, 16, 19, 23, 26}

//go:noinline
func foo(d *decimal) int {
	exp := int(d.d[1])
	if d.dp < 0 || d.dp == 0 && d.d[0] < '5' {
		var n int
		if -d.dp >= len(powtab) {
			n = 27
		} else {
			n = powtab[-d.dp]
		}
		exp += n
	}
	return exp
}

func main() {
	var d decimal
	d.d[0] = '1'
	println("foo(&d)=", foo(&d))
}

GOARCH=arm go run arm.go
panic: runtime error: index out of range [0] with length 9

goroutine 1 [running]:
main.foo(0x202c7ac, 0x0)
	/home/drchase/work/tmp/arm.go:18 +0x78
main.main()
	/home/drchase/work/tmp/arm.go:28 +0x30
exit status 2

=> 0x6c170 <main.foo>:	ldr	r1, [r10, #8]
   0x6c174 <main.foo+4>:	cmp	sp, r1
   0x6c178 <main.foo+8>:	bls	0x6c1ec <main.foo+124>
   0x6c17c <main.foo+12>:	str	lr, [sp, #-12]!
   0x6c180 <main.foo+16>:	ldr	r2, [sp, #16]
   0x6c184 <main.foo+20>:	ldrb	r3, [r2, #1]
   0x6c188 <main.foo+24>:	ldr	r4, [r2, #8]
   0x6c18c <main.foo+28>:	cmp	r4, #0
   0x6c190 <main.foo+32>:	bge	0x6c1cc <main.foo+92>
   0x6c194 <main.foo+36>:	ldr	r11, [pc, #96]	; 0x6c1fc <main.foo+140>
   0x6c198 <main.foo+40>:	ldr	r1, [r11]
   0x6c19c <main.foo+44>:	ldr	r11, [pc, #92]	; 0x6c200 <main.foo+144>
   0x6c1a0 <main.foo+48>:	ldr	r2, [r11]
   0x6c1a4 <main.foo+52>:	cmn	r1, r4
   0x6c1a8 <main.foo+56>:	bgt	0x6c1bc <main.foo+76>
   0x6c1ac <main.foo+60>:	mov	r0, #27
   0x6c1b0 <main.foo+64>:	add	r0, r3, r0
   0x6c1b4 <main.foo+68>:	str	r0, [sp, #20]
   0x6c1b8 <main.foo+72>:	ldr	pc, [sp], #12
   0x6c1bc <main.foo+76>:	rsb	r0, r4, #0
   0x6c1c0 <main.foo+80>:	bls	0x6c1e4 <main.foo+116>
   0x6c1c4 <main.foo+84>:	ldr	r0, [r2, r0, lsl #2]
   0x6c1c8 <main.foo+88>:	b	0x6c1b0 <main.foo+64>
   0x6c1cc <main.foo+92>:	bne	0x6c1dc <main.foo+108>
   0x6c1d0 <main.foo+96>:	ldrb	r2, [r2]
   0x6c1d4 <main.foo+100>:	cmp	r2, #53	; 0x35
   0x6c1d8 <main.foo+104>:	bcc	0x6c194 <main.foo+36>
   0x6c1dc <main.foo+108>:	mov	r0, r3
   0x6c1e0 <main.foo+112>:	b	0x6c1b4 <main.foo+68>
   0x6c1e4 <main.foo+116>:	bl	0x69d50 <runtime.panicIndex>
   0x6c1e8 <main.foo+120>:	andeq	r0, r0, r0
   0x6c1ec <main.foo+124>:	mov	r3, lr
   0x6c1f0 <main.foo+128>:	bl	0x680fc <runtime.morestack_noctxt>
   0x6c1f4 <main.foo+132>:	b	0x6c170 <main.foo>
   0x6c1f8 <main.foo+136>:	b	0x6c1f8 <main.foo+136>
   0x6c1fc <main.foo+140>:	andeq	r1, sp, r4, asr r0
   0x6c200 <main.foo+144>:	andeq	r1, sp, r0, asr r0
   0x6c204 <main.main>:	ldr	r1, [r10, #8]

2: /x $cpsr = 0x80000010
4: /x $r0 = 0x0
5: /x $r1 = 0x9
6: /x $r2 = 0xd0100
7: /x $r3 = 0x0
8: /x $r4 = 0x0
9: x/3i $pc
=> 0x6c1a4 <main.foo+52>:	cmn	r1, r4
   0x6c1a8 <main.foo+56>:	bgt	0x6c1bc <main.foo+76>
   0x6c1ac <main.foo+60>:	mov	r0, #27
(gdb) 
0x0006c1a8	15	in /Users/drchase/work/tmp/arm.go
2: /x $cpsr = 0x10
4: /x $r0 = 0x0
5: /x $r1 = 0x9
6: /x $r2 = 0xd0100
7: /x $r3 = 0x0
8: /x $r4 = 0x0
9: x/3i $pc
=> 0x6c1a8 <main.foo+56>:	bgt	0x6c1bc <main.foo+76>
   0x6c1ac <main.foo+60>:	mov	r0, #27
   0x6c1b0 <main.foo+64>:	add	r0, r3, r0
(gdb) 
0x0006c1bc	22	in /Users/drchase/work/tmp/arm.go
2: /x $cpsr = 0x10
4: /x $r0 = 0x0
5: /x $r1 = 0x9
6: /x $r2 = 0xd0100
7: /x $r3 = 0x0
8: /x $r4 = 0x0
9: x/3i $pc
=> 0x6c1bc <main.foo+76>:	rsb	r0, r4, #0
   0x6c1c0 <main.foo+80>:	bls	0x6c1e4 <main.foo+116>
   0x6c1c4 <main.foo+84>:	ldr	r0, [r2, r0, lsl #2]
(gdb) 
18	in /Users/drchase/work/tmp/arm.go
2: /x $cpsr = 0x10
4: /x $r0 = 0x0
5: /x $r1 = 0x9
6: /x $r2 = 0xd0100
7: /x $r3 = 0x0
8: /x $r4 = 0x0
9: x/3i $pc
=> 0x6c1c0 <main.foo+80>:	bls	0x6c1e4 <main.foo+116>
   0x6c1c4 <main.foo+84>:	ldr	r0, [r2, r0, lsl #2]
   0x6c1c8 <main.foo+88>:	b	0x6c1b0 <main.foo+64>
(gdb) 
0x0006c1e4	18	in /Users/drchase/work/tmp/arm.go
2: /x $cpsr = 0x10
4: /x $r0 = 0x0
5: /x $r1 = 0x9
6: /x $r2 = 0xd0100
7: /x $r3 = 0x0
8: /x $r4 = 0x0
9: x/3i $pc
=> 0x6c1e4 <main.foo+116>:	bl	0x69d50 <runtime.panicIndex>
   0x6c1e8 <main.foo+120>:	andeq	r0, r0, r0
   0x6c1ec <main.foo+124>:	mov	r3, lr