1//go:build gofuzz
 2// +build gofuzz
 3
 4// How to run the fuzzer:
 5//
 6//	$ go get -u github.com/dvyukov/go-fuzz/go-fuzz
 7//	$ go get -u github.com/dvyukov/go-fuzz/go-fuzz-build
 8//	$ go-fuzz-build -libfuzzer -func FuzzReduction -o lib.a
 9//	$ clang -fsanitize=fuzzer lib.a -o fu.exe
10//	$ ./fu.exe
11package fp448
12
13import (
14	"encoding/binary"
15	"fmt"
16	"math/big"
17
18	"github.com/cloudflare/circl/internal/conv"
19)
20
21// FuzzReduction is a fuzzer target for red64 function, which reduces t
22// (112 bits) to a number t' (56 bits) congruent modulo p448.
23func FuzzReduction(data []byte) int {
24	if len(data) != 2*Size {
25		return -1
26	}
27	var got, want Elt
28	var lo, hi [7]uint64
29	a := data[:Size]
30	b := data[Size:]
31	lo[0] = binary.LittleEndian.Uint64(a[0*8 : 1*8])
32	lo[1] = binary.LittleEndian.Uint64(a[1*8 : 2*8])
33	lo[2] = binary.LittleEndian.Uint64(a[2*8 : 3*8])
34	lo[3] = binary.LittleEndian.Uint64(a[3*8 : 4*8])
35	lo[4] = binary.LittleEndian.Uint64(a[4*8 : 5*8])
36	lo[5] = binary.LittleEndian.Uint64(a[5*8 : 6*8])
37	lo[6] = binary.LittleEndian.Uint64(a[6*8 : 7*8])
38
39	hi[0] = binary.LittleEndian.Uint64(b[0*8 : 1*8])
40	hi[1] = binary.LittleEndian.Uint64(b[1*8 : 2*8])
41	hi[2] = binary.LittleEndian.Uint64(b[2*8 : 3*8])
42	hi[3] = binary.LittleEndian.Uint64(b[3*8 : 4*8])
43	hi[4] = binary.LittleEndian.Uint64(b[4*8 : 5*8])
44	hi[5] = binary.LittleEndian.Uint64(b[5*8 : 6*8])
45	hi[6] = binary.LittleEndian.Uint64(b[6*8 : 7*8])
46
47	red64(&got, &lo, &hi)
48
49	t := conv.BytesLe2BigInt(data[:2*Size])
50
51	two448 := big.NewInt(1)
52	two448.Lsh(two448, 448) // 2^448
53	mask448 := big.NewInt(1)
54	mask448.Sub(two448, mask448) // 2^448-1
55	two224plus1 := big.NewInt(1)
56	two224plus1.Lsh(two224plus1, 224)
57	two224plus1.Add(two224plus1, big.NewInt(1)) // 2^224+1
58
59	var loBig, hiBig big.Int
60	for t.Cmp(two448) >= 0 {
61		loBig.And(t, mask448)
62		hiBig.Rsh(t, 448)
63		t.Mul(&hiBig, two224plus1)
64		t.Add(t, &loBig)
65	}
66	conv.BigInt2BytesLe(want[:], t)
67
68	if got != want {
69		fmt.Printf("in:   %v\n", conv.BytesLe2BigInt(data[:2*Size]))
70		fmt.Printf("got:  %v\n", got)
71		fmt.Printf("want: %v\n", want)
72		panic("error found")
73	}
74	return 1
75}