package weakhash

type digest struct {
    buf  []byte
    size int
    a    uint16
    b    uint16
    j    int
}

func (d *digest) Write(data []byte) (int, error) {
    for _, c := range data {
        d.a = d.a - uint16(d.buf[d.j]) + uint16(c)
        d.b = d.b - uint16(d.size)*uint16(d.buf[d.j]) + d.a
        d.buf[d.j] = c
        d.j = (d.j + 1) % d.size
    }
    return len(data), nil
}

jb@syno:~/t/weakhash $ go version
go version go1.7rc6 darwin/amd64
jb@syno:~/t/weakhash $ GOARCH=386 go build
# _/Users/jb/test/weakhash
run compiler with -v for register allocation sites
./weakhash.go:13: internal compiler error: out of fixed registers

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /usr/local/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0x4ff9fa, 0x16, 0x0, 0x0, 0x0)
    /usr/local/go/src/cmd/compile/internal/gc/subr.go:165 +0x248
cmd/compile/internal/gc.Regalloc(0xc42044b320, 0xc420014c30, 0xc42044b200)
    /usr/local/go/src/cmd/compile/internal/gc/gsubr.go:749 +0x16b
cmd/compile/internal/x86.ginscmp(0xc42042183e, 0xc420014c30, 0xc42044b0e0, 0xc42044b200, 0x1, 0x0)
    /usr/local/go/src/cmd/compile/internal/x86/gsubr.go:657 +0x364
cmd/compile/internal/gc.Agenr(0xc4204219e0, 0xc42044aa20, 0xc42044a7e0)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:1245 +0x20e8
cmd/compile/internal/gc.Igen(0xc4204219e0, 0xc42044aa20, 0xc42044a7e0)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:1718 +0x279
cmd/compile/internal/gc.cgen_wb(0xc4204219e0, 0xc42044a7e0, 0xc42040ef00)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:523 +0x2281
cmd/compile/internal/gc.Cgen(0xc4204219e0, 0xc42044a7e0)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:19 +0x3a
cmd/compile/internal/gc.Mgen(0xc4204219e0, 0xc42044a7e0, 0xc42044a750)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:906 +0xf7
cmd/compile/internal/gc.cgen_wb(0xc420421a70, 0xc42044a750, 0x0)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:460 +0x1c95
cmd/compile/internal/gc.Cgen(0xc420421a70, 0xc42044a750)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:19 +0x3a
cmd/compile/internal/gc.cgen_wb(0xc420421b00, 0xc42044a510, 0xc42040ef00)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:738 +0x1045
cmd/compile/internal/gc.Cgen(0xc420421b00, 0xc42044a510)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:19 +0x3a
cmd/compile/internal/gc.cgen_wb(0xc420421cb0, 0xc42044a360, 0x0)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:725 +0xe4c
cmd/compile/internal/gc.Cgen(0xc420421cb0, 0xc42044a360)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:19 +0x3a
cmd/compile/internal/gc.cgen_wb(0xc420421cb0, 0xc420421710, 0x4ef400)
    /usr/local/go/src/cmd/compile/internal/gc/cgen.go:102 +0x427d
cmd/compile/internal/gc.Cgen_as_wb(0xc420421710, 0xc420421cb0, 0xd00000800)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:1023 +0x17b
cmd/compile/internal/gc.Cgen_as(0xc420421710, 0xc420421cb0)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:979 +0x3a
cmd/compile/internal/gc.gen(0xc420421d40)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:926 +0xd6c
cmd/compile/internal/gc.Genlist(0xc4204244c0)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:311 +0x50
cmd/compile/internal/gc.gen(0xc420421560)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:860 +0x62f
cmd/compile/internal/gc.Genlist(0xc420424400)
    /usr/local/go/src/cmd/compile/internal/gc/gen.go:311 +0x50
cmd/compile/internal/gc.genlegacy(0xc4200ec278, 0xc42042c8c0, 0xc42042c930)
    /usr/local/go/src/cmd/compile/internal/gc/pgen.go:498 +0x4d
cmd/compile/internal/gc.compile(0xc4204210e0)
    /usr/local/go/src/cmd/compile/internal/gc/pgen.go:485 +0x7a4
cmd/compile/internal/gc.funccompile(0xc4204210e0)
    /usr/local/go/src/cmd/compile/internal/gc/dcl.go:1287 +0x186
cmd/compile/internal/gc.Main()
    /usr/local/go/src/cmd/compile/internal/gc/main.go:467 +0x19f8
cmd/compile/internal/x86.Main()
    /usr/local/go/src/cmd/compile/internal/x86/galign.go:80 +0x3ba
main.main()
    /usr/local/go/src/cmd/compile/main.go:31 +0x1d4