1 // Copyright 2017 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // +build ignore 6 7 // Generate the constant table associated with the poly used by the 8 // vpmsumd crc32 algorithm. 9 // 10 // go run gen_const_ppc64le.go 11 // 12 // generates crc32_table_ppc64le.s 13 14 // The following is derived from code written by Anton Blanchard 15 // <anton (a] au.ibm.com> found at https://github.com/antonblanchard/crc32-vpmsum. 16 // The original is dual licensed under GPL and Apache 2. As the copyright holder 17 // for the work, IBM has contributed this new work under the golang license. 18 19 // This code was written in Go based on the original C implementation. 20 21 // This is a tool needed to generate the appropriate constants needed for 22 // the vpmsum algorithm. It is included to generate new constant tables if 23 // new polynomial values are included in the future. 24 25 package main 26 27 import ( 28 "bytes" 29 "fmt" 30 "io/ioutil" 31 ) 32 33 var blocking = 32 * 1024 34 35 func reflect_bits(b uint64, nr uint) uint64 { 36 var ref uint64 37 38 for bit := uint64(0); bit < uint64(nr); bit++ { 39 if (b & uint64(1)) == 1 { 40 ref |= (1 << (uint64(nr-1) - bit)) 41 } 42 b = (b >> 1) 43 } 44 return ref 45 } 46 47 func get_remainder(poly uint64, deg uint, n uint) uint64 { 48 49 rem, _ := xnmodp(n, poly, deg) 50 return rem 51 } 52 53 func get_quotient(poly uint64, bits, n uint) uint64 { 54 55 _, div := xnmodp(n, poly, bits) 56 return div 57 } 58 59 // xnmodp returns two values, p and div: 60 // p is the representation of the binary polynomial x**n mod (x ** deg + "poly") 61 // That is p is the binary representation of the modulus polynomial except for its highest-order term. 62 // div is the binary representation of the polynomial x**n / (x ** deg + "poly") 63 func xnmodp(n uint, poly uint64, deg uint) (uint64, uint64) { 64 65 var mod, mask, high, div uint64 66 67 if n < deg { 68 div = 0 69 return poly, div 70 } 71 mask = 1<<deg - 1 72 poly &= mask 73 mod = poly 74 div = 1 75 deg-- 76 n-- 77 for n > deg { 78 high = (mod >> deg) & 1 79 div = (div << 1) | high 80 mod <<= 1 81 if high != 0 { 82 mod ^= poly 83 } 84 n-- 85 } 86 return mod & mask, div 87 } 88 89 func main() { 90 w := new(bytes.Buffer) 91 92 fmt.Fprintf(w, "// autogenerated: do not edit!\n") 93 fmt.Fprintf(w, "// generated from crc32/gen_const_ppc64le.go\n") 94 fmt.Fprintln(w) 95 fmt.Fprintf(w, "#include \"textflag.h\"\n") 96 97 // These are the polynomials supported in vector now. 98 // If adding others, include the polynomial and a name 99 // to identify it. 100 101 genCrc32ConstTable(w, 0xedb88320, "IEEE") 102 genCrc32ConstTable(w, 0x82f63b78, "Cast") 103 genCrc32ConstTable(w, 0xeb31d82e, "Koop") 104 b := w.Bytes() 105 106 err := ioutil.WriteFile("crc32_table_ppc64le.s", b, 0666) 107 if err != nil { 108 fmt.Printf("can't write output: %s\n", err) 109 } 110 } 111 112 func genCrc32ConstTable(w *bytes.Buffer, poly uint32, polyid string) { 113 114 ref_poly := reflect_bits(uint64(poly), 32) 115 fmt.Fprintf(w, "\n\t/* Reduce %d kbits to 1024 bits */\n", blocking*8) 116 j := 0 117 for i := (blocking * 8) - 1024; i > 0; i -= 1024 { 118 a := reflect_bits(get_remainder(ref_poly, 32, uint(i)), 32) << 1 119 b := reflect_bits(get_remainder(ref_poly, 32, uint(i+64)), 32) << 1 120 121 fmt.Fprintf(w, "\t/* x^%d mod p(x)%s, x^%d mod p(x)%s */\n", uint(i+64), "", uint(i), "") 122 fmt.Fprintf(w, "DATA %sConst+%d(SB)/8,$0x%016x\n", polyid, j*8, b) 123 fmt.Fprintf(w, "DATA %sConst+%d(SB)/8,$0x%016x\n", polyid, (j+1)*8, a) 124 125 j += 2 126 fmt.Fprintf(w, "\n") 127 } 128 129 for i := (1024 * 2) - 128; i >= 0; i -= 128 { 130 a := reflect_bits(get_remainder(ref_poly, 32, uint(i+32)), 32) 131 b := reflect_bits(get_remainder(ref_poly, 32, uint(i+64)), 32) 132 c := reflect_bits(get_remainder(ref_poly, 32, uint(i+96)), 32) 133 d := reflect_bits(get_remainder(ref_poly, 32, uint(i+128)), 32) 134 135 fmt.Fprintf(w, "\t/* x^%d mod p(x)%s, x^%d mod p(x)%s, x^%d mod p(x)%s, x^%d mod p(x)%s */\n", i+128, "", i+96, "", i+64, "", i+32, "") 136 fmt.Fprintf(w, "DATA %sConst+%d(SB)/8,$0x%08x%08x\n", polyid, j*8, c, d) 137 fmt.Fprintf(w, "DATA %sConst+%d(SB)/8,$0x%08x%08x\n", polyid, (j+1)*8, a, b) 138 139 j += 2 140 fmt.Fprintf(w, "\n") 141 } 142 143 fmt.Fprintf(w, "GLOBL %sConst(SB),RODATA,$4336\n", polyid) 144 fmt.Fprintf(w, "\n /* Barrett constant m - (4^32)/n */\n") 145 fmt.Fprintf(w, "DATA %sBarConst(SB)/8,$0x%016x\n", polyid, reflect_bits(get_quotient(ref_poly, 32, 64), 33)) 146 fmt.Fprintf(w, "DATA %sBarConst+8(SB)/8,$0x0000000000000000\n", polyid) 147 fmt.Fprintf(w, "DATA %sBarConst+16(SB)/8,$0x%016x\n", polyid, reflect_bits((uint64(1)<<32)|ref_poly, 33)) // reflected? 148 fmt.Fprintf(w, "DATA %sBarConst+24(SB)/8,$0x0000000000000000\n", polyid) 149 fmt.Fprintf(w, "GLOBL %sBarConst(SB),RODATA,$32\n", polyid) 150 } 151
