tlog.app/go/errors@v0.9.0/unsafe_fmt.go (about) 1 package errors 2 3 import ( 4 "fmt" 5 "io" 6 "strconv" 7 "unsafe" 8 ) 9 10 func subPrintArg(s fmt.State, arg interface{}, verb rune) { 11 i := *(*iface)(unsafe.Pointer(&s)) 12 if i.typ != ppType { 13 var buf [64]byte 14 15 i := 0 16 17 buf[i] = '%' 18 i++ 19 20 for _, f := range "-+# 0" { 21 if s.Flag(int(f)) { 22 buf[i] = byte(f) 23 i++ 24 } 25 } 26 27 if w, ok := s.Width(); ok { 28 q := strconv.AppendInt(buf[:i], int64(w), 10) 29 i = len(q) 30 } 31 32 if p, ok := s.Precision(); ok { 33 buf[i] = '.' 34 i++ 35 36 q := strconv.AppendInt(buf[:i], int64(p), 10) 37 i = len(q) 38 } 39 40 buf[i] = byte(verb) 41 i++ 42 43 fmt.Fprintf(s, bytesToString(buf[:i]), arg) 44 45 return 46 } 47 48 printArg(i.word, arg, verb) 49 } 50 51 type ( 52 iface struct { 53 typ, word unsafe.Pointer 54 } 55 56 formatter struct{} 57 ) 58 59 var ppType unsafe.Pointer 60 61 func init() { 62 fmt.Fprintf(io.Discard, "%v", formatter{}) 63 } 64 65 //go:linkname printArg fmt.(*pp).printArg 66 func printArg(p unsafe.Pointer, arg interface{}, verb rune) 67 68 //go:linkname newPrinter fmt.newPrinter 69 func newPrinter() unsafe.Pointer 70 71 //go:linkname ppFree fmt.(*pp).free 72 func ppFree(unsafe.Pointer) 73 74 func (formatter) Format(s fmt.State, _ rune) { 75 i := *(*iface)(unsafe.Pointer(&s)) 76 77 ppType = i.typ 78 } 79 80 func bytesToString(b []byte) string { 81 return *(*string)(unsafe.Pointer(&b)) 82 }