github.com/rsc/tmp@v0.0.0-20240517235954-6deaab19748b/bootstrap/internal/gc/big/rat_test.go (about)

     1  // Do not edit. Bootstrap copy of /Users/rsc/g/go/src/cmd/internal/gc/big/rat_test.go
     2  
     3  // Copyright 2010 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package big
     8  
     9  import (
    10  	"bytes"
    11  	"encoding/gob"
    12  	"encoding/json"
    13  	"encoding/xml"
    14  	"math"
    15  	"testing"
    16  )
    17  
    18  func TestZeroRat(t *testing.T) {
    19  	var x, y, z Rat
    20  	y.SetFrac64(0, 42)
    21  
    22  	if x.Cmp(&y) != 0 {
    23  		t.Errorf("x and y should be both equal and zero")
    24  	}
    25  
    26  	if s := x.String(); s != "0/1" {
    27  		t.Errorf("got x = %s, want 0/1", s)
    28  	}
    29  
    30  	if s := x.RatString(); s != "0" {
    31  		t.Errorf("got x = %s, want 0", s)
    32  	}
    33  
    34  	z.Add(&x, &y)
    35  	if s := z.RatString(); s != "0" {
    36  		t.Errorf("got x+y = %s, want 0", s)
    37  	}
    38  
    39  	z.Sub(&x, &y)
    40  	if s := z.RatString(); s != "0" {
    41  		t.Errorf("got x-y = %s, want 0", s)
    42  	}
    43  
    44  	z.Mul(&x, &y)
    45  	if s := z.RatString(); s != "0" {
    46  		t.Errorf("got x*y = %s, want 0", s)
    47  	}
    48  
    49  	// check for division by zero
    50  	defer func() {
    51  		if s := recover(); s == nil || s.(string) != "division by zero" {
    52  			panic(s)
    53  		}
    54  	}()
    55  	z.Quo(&x, &y)
    56  }
    57  
    58  func TestRatSign(t *testing.T) {
    59  	zero := NewRat(0, 1)
    60  	for _, a := range setStringTests {
    61  		x, ok := new(Rat).SetString(a.in)
    62  		if !ok {
    63  			continue
    64  		}
    65  		s := x.Sign()
    66  		e := x.Cmp(zero)
    67  		if s != e {
    68  			t.Errorf("got %d; want %d for z = %v", s, e, &x)
    69  		}
    70  	}
    71  }
    72  
    73  var ratCmpTests = []struct {
    74  	rat1, rat2 string
    75  	out        int
    76  }{
    77  	{"0", "0/1", 0},
    78  	{"1/1", "1", 0},
    79  	{"-1", "-2/2", 0},
    80  	{"1", "0", 1},
    81  	{"0/1", "1/1", -1},
    82  	{"-5/1434770811533343057144", "-5/1434770811533343057145", -1},
    83  	{"49832350382626108453/8964749413", "49832350382626108454/8964749413", -1},
    84  	{"-37414950961700930/7204075375675961", "37414950961700930/7204075375675961", -1},
    85  	{"37414950961700930/7204075375675961", "74829901923401860/14408150751351922", 0},
    86  }
    87  
    88  func TestRatCmp(t *testing.T) {
    89  	for i, test := range ratCmpTests {
    90  		x, _ := new(Rat).SetString(test.rat1)
    91  		y, _ := new(Rat).SetString(test.rat2)
    92  
    93  		out := x.Cmp(y)
    94  		if out != test.out {
    95  			t.Errorf("#%d got out = %v; want %v", i, out, test.out)
    96  		}
    97  	}
    98  }
    99  
   100  func TestIsInt(t *testing.T) {
   101  	one := NewInt(1)
   102  	for _, a := range setStringTests {
   103  		x, ok := new(Rat).SetString(a.in)
   104  		if !ok {
   105  			continue
   106  		}
   107  		i := x.IsInt()
   108  		e := x.Denom().Cmp(one) == 0
   109  		if i != e {
   110  			t.Errorf("got IsInt(%v) == %v; want %v", x, i, e)
   111  		}
   112  	}
   113  }
   114  
   115  func TestRatAbs(t *testing.T) {
   116  	zero := new(Rat)
   117  	for _, a := range setStringTests {
   118  		x, ok := new(Rat).SetString(a.in)
   119  		if !ok {
   120  			continue
   121  		}
   122  		e := new(Rat).Set(x)
   123  		if e.Cmp(zero) < 0 {
   124  			e.Sub(zero, e)
   125  		}
   126  		z := new(Rat).Abs(x)
   127  		if z.Cmp(e) != 0 {
   128  			t.Errorf("got Abs(%v) = %v; want %v", x, z, e)
   129  		}
   130  	}
   131  }
   132  
   133  func TestRatNeg(t *testing.T) {
   134  	zero := new(Rat)
   135  	for _, a := range setStringTests {
   136  		x, ok := new(Rat).SetString(a.in)
   137  		if !ok {
   138  			continue
   139  		}
   140  		e := new(Rat).Sub(zero, x)
   141  		z := new(Rat).Neg(x)
   142  		if z.Cmp(e) != 0 {
   143  			t.Errorf("got Neg(%v) = %v; want %v", x, z, e)
   144  		}
   145  	}
   146  }
   147  
   148  func TestRatInv(t *testing.T) {
   149  	zero := new(Rat)
   150  	for _, a := range setStringTests {
   151  		x, ok := new(Rat).SetString(a.in)
   152  		if !ok {
   153  			continue
   154  		}
   155  		if x.Cmp(zero) == 0 {
   156  			continue // avoid division by zero
   157  		}
   158  		e := new(Rat).SetFrac(x.Denom(), x.Num())
   159  		z := new(Rat).Inv(x)
   160  		if z.Cmp(e) != 0 {
   161  			t.Errorf("got Inv(%v) = %v; want %v", x, z, e)
   162  		}
   163  	}
   164  }
   165  
   166  type ratBinFun func(z, x, y *Rat) *Rat
   167  type ratBinArg struct {
   168  	x, y, z string
   169  }
   170  
   171  func testRatBin(t *testing.T, i int, name string, f ratBinFun, a ratBinArg) {
   172  	x, _ := new(Rat).SetString(a.x)
   173  	y, _ := new(Rat).SetString(a.y)
   174  	z, _ := new(Rat).SetString(a.z)
   175  	out := f(new(Rat), x, y)
   176  
   177  	if out.Cmp(z) != 0 {
   178  		t.Errorf("%s #%d got %s want %s", name, i, out, z)
   179  	}
   180  }
   181  
   182  var ratBinTests = []struct {
   183  	x, y      string
   184  	sum, prod string
   185  }{
   186  	{"0", "0", "0", "0"},
   187  	{"0", "1", "1", "0"},
   188  	{"-1", "0", "-1", "0"},
   189  	{"-1", "1", "0", "-1"},
   190  	{"1", "1", "2", "1"},
   191  	{"1/2", "1/2", "1", "1/4"},
   192  	{"1/4", "1/3", "7/12", "1/12"},
   193  	{"2/5", "-14/3", "-64/15", "-28/15"},
   194  	{"4707/49292519774798173060", "-3367/70976135186689855734", "84058377121001851123459/1749296273614329067191168098769082663020", "-1760941/388732505247628681598037355282018369560"},
   195  	{"-61204110018146728334/3", "-31052192278051565633/2", "-215564796870448153567/6", "950260896245257153059642991192710872711/3"},
   196  	{"-854857841473707320655/4237645934602118692642972629634714039", "-18/31750379913563777419", "-27/133467566250814981", "15387441146526731771790/134546868362786310073779084329032722548987800600710485341"},
   197  	{"618575745270541348005638912139/19198433543745179392300736", "-19948846211000086/637313996471", "27674141753240653/30123979153216", "-6169936206128396568797607742807090270137721977/6117715203873571641674006593837351328"},
   198  	{"-3/26206484091896184128", "5/2848423294177090248", "15310893822118706237/9330894968229805033368778458685147968", "-5/24882386581946146755650075889827061248"},
   199  	{"26946729/330400702820", "41563965/225583428284", "1238218672302860271/4658307703098666660055", "224002580204097/14906584649915733312176"},
   200  	{"-8259900599013409474/7", "-84829337473700364773/56707961321161574960", "-468402123685491748914621885145127724451/396955729248131024720", "350340947706464153265156004876107029701/198477864624065512360"},
   201  	{"575775209696864/1320203974639986246357", "29/712593081308", "410331716733912717985762465/940768218243776489278275419794956", "808/45524274987585732633"},
   202  	{"1786597389946320496771/2066653520653241", "6269770/1992362624741777", "3559549865190272133656109052308126637/4117523232840525481453983149257", "8967230/3296219033"},
   203  	{"-36459180403360509753/32150500941194292113930", "9381566963714/9633539", "301622077145533298008420642898530153/309723104686531919656937098270", "-3784609207827/3426986245"},
   204  }
   205  
   206  func TestRatBin(t *testing.T) {
   207  	for i, test := range ratBinTests {
   208  		arg := ratBinArg{test.x, test.y, test.sum}
   209  		testRatBin(t, i, "Add", (*Rat).Add, arg)
   210  
   211  		arg = ratBinArg{test.y, test.x, test.sum}
   212  		testRatBin(t, i, "Add symmetric", (*Rat).Add, arg)
   213  
   214  		arg = ratBinArg{test.sum, test.x, test.y}
   215  		testRatBin(t, i, "Sub", (*Rat).Sub, arg)
   216  
   217  		arg = ratBinArg{test.sum, test.y, test.x}
   218  		testRatBin(t, i, "Sub symmetric", (*Rat).Sub, arg)
   219  
   220  		arg = ratBinArg{test.x, test.y, test.prod}
   221  		testRatBin(t, i, "Mul", (*Rat).Mul, arg)
   222  
   223  		arg = ratBinArg{test.y, test.x, test.prod}
   224  		testRatBin(t, i, "Mul symmetric", (*Rat).Mul, arg)
   225  
   226  		if test.x != "0" {
   227  			arg = ratBinArg{test.prod, test.x, test.y}
   228  			testRatBin(t, i, "Quo", (*Rat).Quo, arg)
   229  		}
   230  
   231  		if test.y != "0" {
   232  			arg = ratBinArg{test.prod, test.y, test.x}
   233  			testRatBin(t, i, "Quo symmetric", (*Rat).Quo, arg)
   234  		}
   235  	}
   236  }
   237  
   238  func TestIssue820(t *testing.T) {
   239  	x := NewRat(3, 1)
   240  	y := NewRat(2, 1)
   241  	z := y.Quo(x, y)
   242  	q := NewRat(3, 2)
   243  	if z.Cmp(q) != 0 {
   244  		t.Errorf("got %s want %s", z, q)
   245  	}
   246  
   247  	y = NewRat(3, 1)
   248  	x = NewRat(2, 1)
   249  	z = y.Quo(x, y)
   250  	q = NewRat(2, 3)
   251  	if z.Cmp(q) != 0 {
   252  		t.Errorf("got %s want %s", z, q)
   253  	}
   254  
   255  	x = NewRat(3, 1)
   256  	z = x.Quo(x, x)
   257  	q = NewRat(3, 3)
   258  	if z.Cmp(q) != 0 {
   259  		t.Errorf("got %s want %s", z, q)
   260  	}
   261  }
   262  
   263  var setFrac64Tests = []struct {
   264  	a, b int64
   265  	out  string
   266  }{
   267  	{0, 1, "0"},
   268  	{0, -1, "0"},
   269  	{1, 1, "1"},
   270  	{-1, 1, "-1"},
   271  	{1, -1, "-1"},
   272  	{-1, -1, "1"},
   273  	{-9223372036854775808, -9223372036854775808, "1"},
   274  }
   275  
   276  func TestRatSetFrac64Rat(t *testing.T) {
   277  	for i, test := range setFrac64Tests {
   278  		x := new(Rat).SetFrac64(test.a, test.b)
   279  		if x.RatString() != test.out {
   280  			t.Errorf("#%d got %s want %s", i, x.RatString(), test.out)
   281  		}
   282  	}
   283  }
   284  
   285  func TestRatGobEncoding(t *testing.T) {
   286  	var medium bytes.Buffer
   287  	enc := gob.NewEncoder(&medium)
   288  	dec := gob.NewDecoder(&medium)
   289  	for _, test := range encodingTests {
   290  		medium.Reset() // empty buffer for each test case (in case of failures)
   291  		var tx Rat
   292  		tx.SetString(test + ".14159265")
   293  		if err := enc.Encode(&tx); err != nil {
   294  			t.Errorf("encoding of %s failed: %s", &tx, err)
   295  		}
   296  		var rx Rat
   297  		if err := dec.Decode(&rx); err != nil {
   298  			t.Errorf("decoding of %s failed: %s", &tx, err)
   299  		}
   300  		if rx.Cmp(&tx) != 0 {
   301  			t.Errorf("transmission of %s failed: got %s want %s", &tx, &rx, &tx)
   302  		}
   303  	}
   304  }
   305  
   306  // Sending a nil Rat pointer (inside a slice) on a round trip through gob should yield a zero.
   307  // TODO: top-level nils.
   308  func TestGobEncodingNilRatInSlice(t *testing.T) {
   309  	buf := new(bytes.Buffer)
   310  	enc := gob.NewEncoder(buf)
   311  	dec := gob.NewDecoder(buf)
   312  
   313  	var in = make([]*Rat, 1)
   314  	err := enc.Encode(&in)
   315  	if err != nil {
   316  		t.Errorf("gob encode failed: %q", err)
   317  	}
   318  	var out []*Rat
   319  	err = dec.Decode(&out)
   320  	if err != nil {
   321  		t.Fatalf("gob decode failed: %q", err)
   322  	}
   323  	if len(out) != 1 {
   324  		t.Fatalf("wrong len; want 1 got %d", len(out))
   325  	}
   326  	var zero Rat
   327  	if out[0].Cmp(&zero) != 0 {
   328  		t.Errorf("transmission of (*Int)(nill) failed: got %s want 0", out)
   329  	}
   330  }
   331  
   332  var ratNums = []string{
   333  	"-141592653589793238462643383279502884197169399375105820974944592307816406286",
   334  	"-1415926535897932384626433832795028841971",
   335  	"-141592653589793",
   336  	"-1",
   337  	"0",
   338  	"1",
   339  	"141592653589793",
   340  	"1415926535897932384626433832795028841971",
   341  	"141592653589793238462643383279502884197169399375105820974944592307816406286",
   342  }
   343  
   344  var ratDenoms = []string{
   345  	"1",
   346  	"718281828459045",
   347  	"7182818284590452353602874713526624977572",
   348  	"718281828459045235360287471352662497757247093699959574966967627724076630353",
   349  }
   350  
   351  func TestRatJSONEncoding(t *testing.T) {
   352  	for _, num := range ratNums {
   353  		for _, denom := range ratDenoms {
   354  			var tx Rat
   355  			tx.SetString(num + "/" + denom)
   356  			b, err := json.Marshal(&tx)
   357  			if err != nil {
   358  				t.Errorf("marshaling of %s failed: %s", &tx, err)
   359  				continue
   360  			}
   361  			var rx Rat
   362  			if err := json.Unmarshal(b, &rx); err != nil {
   363  				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
   364  				continue
   365  			}
   366  			if rx.Cmp(&tx) != 0 {
   367  				t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
   368  			}
   369  		}
   370  	}
   371  }
   372  
   373  func TestRatXMLEncoding(t *testing.T) {
   374  	for _, num := range ratNums {
   375  		for _, denom := range ratDenoms {
   376  			var tx Rat
   377  			tx.SetString(num + "/" + denom)
   378  			b, err := xml.Marshal(&tx)
   379  			if err != nil {
   380  				t.Errorf("marshaling of %s failed: %s", &tx, err)
   381  				continue
   382  			}
   383  			var rx Rat
   384  			if err := xml.Unmarshal(b, &rx); err != nil {
   385  				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
   386  				continue
   387  			}
   388  			if rx.Cmp(&tx) != 0 {
   389  				t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
   390  			}
   391  		}
   392  	}
   393  }
   394  
   395  func TestIssue2379(t *testing.T) {
   396  	// 1) no aliasing
   397  	q := NewRat(3, 2)
   398  	x := new(Rat)
   399  	x.SetFrac(NewInt(3), NewInt(2))
   400  	if x.Cmp(q) != 0 {
   401  		t.Errorf("1) got %s want %s", x, q)
   402  	}
   403  
   404  	// 2) aliasing of numerator
   405  	x = NewRat(2, 3)
   406  	x.SetFrac(NewInt(3), x.Num())
   407  	if x.Cmp(q) != 0 {
   408  		t.Errorf("2) got %s want %s", x, q)
   409  	}
   410  
   411  	// 3) aliasing of denominator
   412  	x = NewRat(2, 3)
   413  	x.SetFrac(x.Denom(), NewInt(2))
   414  	if x.Cmp(q) != 0 {
   415  		t.Errorf("3) got %s want %s", x, q)
   416  	}
   417  
   418  	// 4) aliasing of numerator and denominator
   419  	x = NewRat(2, 3)
   420  	x.SetFrac(x.Denom(), x.Num())
   421  	if x.Cmp(q) != 0 {
   422  		t.Errorf("4) got %s want %s", x, q)
   423  	}
   424  
   425  	// 5) numerator and denominator are the same
   426  	q = NewRat(1, 1)
   427  	x = new(Rat)
   428  	n := NewInt(7)
   429  	x.SetFrac(n, n)
   430  	if x.Cmp(q) != 0 {
   431  		t.Errorf("5) got %s want %s", x, q)
   432  	}
   433  }
   434  
   435  func TestIssue3521(t *testing.T) {
   436  	a := new(Int)
   437  	b := new(Int)
   438  	a.SetString("64375784358435883458348587", 0)
   439  	b.SetString("4789759874531", 0)
   440  
   441  	// 0) a raw zero value has 1 as denominator
   442  	zero := new(Rat)
   443  	one := NewInt(1)
   444  	if zero.Denom().Cmp(one) != 0 {
   445  		t.Errorf("0) got %s want %s", zero.Denom(), one)
   446  	}
   447  
   448  	// 1a) a zero value remains zero independent of denominator
   449  	x := new(Rat)
   450  	x.Denom().Set(new(Int).Neg(b))
   451  	if x.Cmp(zero) != 0 {
   452  		t.Errorf("1a) got %s want %s", x, zero)
   453  	}
   454  
   455  	// 1b) a zero value may have a denominator != 0 and != 1
   456  	x.Num().Set(a)
   457  	qab := new(Rat).SetFrac(a, b)
   458  	if x.Cmp(qab) != 0 {
   459  		t.Errorf("1b) got %s want %s", x, qab)
   460  	}
   461  
   462  	// 2a) an integral value becomes a fraction depending on denominator
   463  	x.SetFrac64(10, 2)
   464  	x.Denom().SetInt64(3)
   465  	q53 := NewRat(5, 3)
   466  	if x.Cmp(q53) != 0 {
   467  		t.Errorf("2a) got %s want %s", x, q53)
   468  	}
   469  
   470  	// 2b) an integral value becomes a fraction depending on denominator
   471  	x = NewRat(10, 2)
   472  	x.Denom().SetInt64(3)
   473  	if x.Cmp(q53) != 0 {
   474  		t.Errorf("2b) got %s want %s", x, q53)
   475  	}
   476  
   477  	// 3) changing the numerator/denominator of a Rat changes the Rat
   478  	x.SetFrac(a, b)
   479  	a = x.Num()
   480  	b = x.Denom()
   481  	a.SetInt64(5)
   482  	b.SetInt64(3)
   483  	if x.Cmp(q53) != 0 {
   484  		t.Errorf("3) got %s want %s", x, q53)
   485  	}
   486  }
   487  
   488  func TestFloat32Distribution(t *testing.T) {
   489  	// Generate a distribution of (sign, mantissa, exp) values
   490  	// broader than the float32 range, and check Rat.Float32()
   491  	// always picks the closest float32 approximation.
   492  	var add = []int64{
   493  		0,
   494  		1,
   495  		3,
   496  		5,
   497  		7,
   498  		9,
   499  		11,
   500  	}
   501  	var winc, einc = uint64(1), 1 // soak test (~1.5s on x86-64)
   502  	if testing.Short() {
   503  		winc, einc = 5, 15 // quick test (~60ms on x86-64)
   504  	}
   505  
   506  	for _, sign := range "+-" {
   507  		for _, a := range add {
   508  			for wid := uint64(0); wid < 30; wid += winc {
   509  				b := 1<<wid + a
   510  				if sign == '-' {
   511  					b = -b
   512  				}
   513  				for exp := -150; exp < 150; exp += einc {
   514  					num, den := NewInt(b), NewInt(1)
   515  					if exp > 0 {
   516  						num.Lsh(num, uint(exp))
   517  					} else {
   518  						den.Lsh(den, uint(-exp))
   519  					}
   520  					r := new(Rat).SetFrac(num, den)
   521  					f, _ := r.Float32()
   522  
   523  					if !checkIsBestApprox32(t, f, r) {
   524  						// Append context information.
   525  						t.Errorf("(input was mantissa %#x, exp %d; f = %g (%b); f ~ %g; r = %v)",
   526  							b, exp, f, f, math.Ldexp(float64(b), exp), r)
   527  					}
   528  
   529  					checkNonLossyRoundtrip32(t, f)
   530  				}
   531  			}
   532  		}
   533  	}
   534  }
   535  
   536  func TestFloat64Distribution(t *testing.T) {
   537  	// Generate a distribution of (sign, mantissa, exp) values
   538  	// broader than the float64 range, and check Rat.Float64()
   539  	// always picks the closest float64 approximation.
   540  	var add = []int64{
   541  		0,
   542  		1,
   543  		3,
   544  		5,
   545  		7,
   546  		9,
   547  		11,
   548  	}
   549  	var winc, einc = uint64(1), 1 // soak test (~75s on x86-64)
   550  	if testing.Short() {
   551  		winc, einc = 10, 500 // quick test (~12ms on x86-64)
   552  	}
   553  
   554  	for _, sign := range "+-" {
   555  		for _, a := range add {
   556  			for wid := uint64(0); wid < 60; wid += winc {
   557  				b := 1<<wid + a
   558  				if sign == '-' {
   559  					b = -b
   560  				}
   561  				for exp := -1100; exp < 1100; exp += einc {
   562  					num, den := NewInt(b), NewInt(1)
   563  					if exp > 0 {
   564  						num.Lsh(num, uint(exp))
   565  					} else {
   566  						den.Lsh(den, uint(-exp))
   567  					}
   568  					r := new(Rat).SetFrac(num, den)
   569  					f, _ := r.Float64()
   570  
   571  					if !checkIsBestApprox64(t, f, r) {
   572  						// Append context information.
   573  						t.Errorf("(input was mantissa %#x, exp %d; f = %g (%b); f ~ %g; r = %v)",
   574  							b, exp, f, f, math.Ldexp(float64(b), exp), r)
   575  					}
   576  
   577  					checkNonLossyRoundtrip64(t, f)
   578  				}
   579  			}
   580  		}
   581  	}
   582  }
   583  
   584  // TestSetFloat64NonFinite checks that SetFloat64 of a non-finite value
   585  // returns nil.
   586  func TestSetFloat64NonFinite(t *testing.T) {
   587  	for _, f := range []float64{math.NaN(), math.Inf(+1), math.Inf(-1)} {
   588  		var r Rat
   589  		if r2 := r.SetFloat64(f); r2 != nil {
   590  			t.Errorf("SetFloat64(%g) was %v, want nil", f, r2)
   591  		}
   592  	}
   593  }
   594  
   595  // checkNonLossyRoundtrip32 checks that a float->Rat->float roundtrip is
   596  // non-lossy for finite f.
   597  func checkNonLossyRoundtrip32(t *testing.T, f float32) {
   598  	if !isFinite(float64(f)) {
   599  		return
   600  	}
   601  	r := new(Rat).SetFloat64(float64(f))
   602  	if r == nil {
   603  		t.Errorf("Rat.SetFloat64(float64(%g) (%b)) == nil", f, f)
   604  		return
   605  	}
   606  	f2, exact := r.Float32()
   607  	if f != f2 || !exact {
   608  		t.Errorf("Rat.SetFloat64(float64(%g)).Float32() = %g (%b), %v, want %g (%b), %v; delta = %b",
   609  			f, f2, f2, exact, f, f, true, f2-f)
   610  	}
   611  }
   612  
   613  // checkNonLossyRoundtrip64 checks that a float->Rat->float roundtrip is
   614  // non-lossy for finite f.
   615  func checkNonLossyRoundtrip64(t *testing.T, f float64) {
   616  	if !isFinite(f) {
   617  		return
   618  	}
   619  	r := new(Rat).SetFloat64(f)
   620  	if r == nil {
   621  		t.Errorf("Rat.SetFloat64(%g (%b)) == nil", f, f)
   622  		return
   623  	}
   624  	f2, exact := r.Float64()
   625  	if f != f2 || !exact {
   626  		t.Errorf("Rat.SetFloat64(%g).Float64() = %g (%b), %v, want %g (%b), %v; delta = %b",
   627  			f, f2, f2, exact, f, f, true, f2-f)
   628  	}
   629  }
   630  
   631  // delta returns the absolute difference between r and f.
   632  func delta(r *Rat, f float64) *Rat {
   633  	d := new(Rat).Sub(r, new(Rat).SetFloat64(f))
   634  	return d.Abs(d)
   635  }
   636  
   637  // checkIsBestApprox32 checks that f is the best possible float32
   638  // approximation of r.
   639  // Returns true on success.
   640  func checkIsBestApprox32(t *testing.T, f float32, r *Rat) bool {
   641  	if math.Abs(float64(f)) >= math.MaxFloat32 {
   642  		// Cannot check +Inf, -Inf, nor the float next to them (MaxFloat32).
   643  		// But we have tests for these special cases.
   644  		return true
   645  	}
   646  
   647  	// r must be strictly between f0 and f1, the floats bracketing f.
   648  	f0 := math.Nextafter32(f, float32(math.Inf(-1)))
   649  	f1 := math.Nextafter32(f, float32(math.Inf(+1)))
   650  
   651  	// For f to be correct, r must be closer to f than to f0 or f1.
   652  	df := delta(r, float64(f))
   653  	df0 := delta(r, float64(f0))
   654  	df1 := delta(r, float64(f1))
   655  	if df.Cmp(df0) > 0 {
   656  		t.Errorf("Rat(%v).Float32() = %g (%b), but previous float32 %g (%b) is closer", r, f, f, f0, f0)
   657  		return false
   658  	}
   659  	if df.Cmp(df1) > 0 {
   660  		t.Errorf("Rat(%v).Float32() = %g (%b), but next float32 %g (%b) is closer", r, f, f, f1, f1)
   661  		return false
   662  	}
   663  	if df.Cmp(df0) == 0 && !isEven32(f) {
   664  		t.Errorf("Rat(%v).Float32() = %g (%b); halfway should have rounded to %g (%b) instead", r, f, f, f0, f0)
   665  		return false
   666  	}
   667  	if df.Cmp(df1) == 0 && !isEven32(f) {
   668  		t.Errorf("Rat(%v).Float32() = %g (%b); halfway should have rounded to %g (%b) instead", r, f, f, f1, f1)
   669  		return false
   670  	}
   671  	return true
   672  }
   673  
   674  // checkIsBestApprox64 checks that f is the best possible float64
   675  // approximation of r.
   676  // Returns true on success.
   677  func checkIsBestApprox64(t *testing.T, f float64, r *Rat) bool {
   678  	if math.Abs(f) >= math.MaxFloat64 {
   679  		// Cannot check +Inf, -Inf, nor the float next to them (MaxFloat64).
   680  		// But we have tests for these special cases.
   681  		return true
   682  	}
   683  
   684  	// r must be strictly between f0 and f1, the floats bracketing f.
   685  	f0 := math.Nextafter(f, math.Inf(-1))
   686  	f1 := math.Nextafter(f, math.Inf(+1))
   687  
   688  	// For f to be correct, r must be closer to f than to f0 or f1.
   689  	df := delta(r, f)
   690  	df0 := delta(r, f0)
   691  	df1 := delta(r, f1)
   692  	if df.Cmp(df0) > 0 {
   693  		t.Errorf("Rat(%v).Float64() = %g (%b), but previous float64 %g (%b) is closer", r, f, f, f0, f0)
   694  		return false
   695  	}
   696  	if df.Cmp(df1) > 0 {
   697  		t.Errorf("Rat(%v).Float64() = %g (%b), but next float64 %g (%b) is closer", r, f, f, f1, f1)
   698  		return false
   699  	}
   700  	if df.Cmp(df0) == 0 && !isEven64(f) {
   701  		t.Errorf("Rat(%v).Float64() = %g (%b); halfway should have rounded to %g (%b) instead", r, f, f, f0, f0)
   702  		return false
   703  	}
   704  	if df.Cmp(df1) == 0 && !isEven64(f) {
   705  		t.Errorf("Rat(%v).Float64() = %g (%b); halfway should have rounded to %g (%b) instead", r, f, f, f1, f1)
   706  		return false
   707  	}
   708  	return true
   709  }
   710  
   711  func isEven32(f float32) bool { return math.Float32bits(f)&1 == 0 }
   712  func isEven64(f float64) bool { return math.Float64bits(f)&1 == 0 }
   713  
   714  func TestIsFinite(t *testing.T) {
   715  	finites := []float64{
   716  		1.0 / 3,
   717  		4891559871276714924261e+222,
   718  		math.MaxFloat64,
   719  		math.SmallestNonzeroFloat64,
   720  		-math.MaxFloat64,
   721  		-math.SmallestNonzeroFloat64,
   722  	}
   723  	for _, f := range finites {
   724  		if !isFinite(f) {
   725  			t.Errorf("!IsFinite(%g (%b))", f, f)
   726  		}
   727  	}
   728  	nonfinites := []float64{
   729  		math.NaN(),
   730  		math.Inf(-1),
   731  		math.Inf(+1),
   732  	}
   733  	for _, f := range nonfinites {
   734  		if isFinite(f) {
   735  			t.Errorf("IsFinite(%g, (%b))", f, f)
   736  		}
   737  	}
   738  }