Source file src/runtime/softfloat64.go

Documentation: runtime

		 1  // Copyright 2010 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  // Software IEEE754 64-bit floating point.
		 6  // Only referred to (and thus linked in) by arm port
		 7  // and by tests in this directory.
		 8  
		 9  package runtime
		10  
		11  const (
		12  	mantbits64 uint = 52
		13  	expbits64	uint = 11
		14  	bias64					= -1<<(expbits64-1) + 1
		15  
		16  	nan64 uint64 = (1<<expbits64-1)<<mantbits64 + 1<<(mantbits64-1) // quiet NaN, 0 payload
		17  	inf64 uint64 = (1<<expbits64 - 1) << mantbits64
		18  	neg64 uint64 = 1 << (expbits64 + mantbits64)
		19  
		20  	mantbits32 uint = 23
		21  	expbits32	uint = 8
		22  	bias32					= -1<<(expbits32-1) + 1
		23  
		24  	nan32 uint32 = (1<<expbits32-1)<<mantbits32 + 1<<(mantbits32-1) // quiet NaN, 0 payload
		25  	inf32 uint32 = (1<<expbits32 - 1) << mantbits32
		26  	neg32 uint32 = 1 << (expbits32 + mantbits32)
		27  )
		28  
		29  func funpack64(f uint64) (sign, mant uint64, exp int, inf, nan bool) {
		30  	sign = f & (1 << (mantbits64 + expbits64))
		31  	mant = f & (1<<mantbits64 - 1)
		32  	exp = int(f>>mantbits64) & (1<<expbits64 - 1)
		33  
		34  	switch exp {
		35  	case 1<<expbits64 - 1:
		36  		if mant != 0 {
		37  			nan = true
		38  			return
		39  		}
		40  		inf = true
		41  		return
		42  
		43  	case 0:
		44  		// denormalized
		45  		if mant != 0 {
		46  			exp += bias64 + 1
		47  			for mant < 1<<mantbits64 {
		48  				mant <<= 1
		49  				exp--
		50  			}
		51  		}
		52  
		53  	default:
		54  		// add implicit top bit
		55  		mant |= 1 << mantbits64
		56  		exp += bias64
		57  	}
		58  	return
		59  }
		60  
		61  func funpack32(f uint32) (sign, mant uint32, exp int, inf, nan bool) {
		62  	sign = f & (1 << (mantbits32 + expbits32))
		63  	mant = f & (1<<mantbits32 - 1)
		64  	exp = int(f>>mantbits32) & (1<<expbits32 - 1)
		65  
		66  	switch exp {
		67  	case 1<<expbits32 - 1:
		68  		if mant != 0 {
		69  			nan = true
		70  			return
		71  		}
		72  		inf = true
		73  		return
		74  
		75  	case 0:
		76  		// denormalized
		77  		if mant != 0 {
		78  			exp += bias32 + 1
		79  			for mant < 1<<mantbits32 {
		80  				mant <<= 1
		81  				exp--
		82  			}
		83  		}
		84  
		85  	default:
		86  		// add implicit top bit
		87  		mant |= 1 << mantbits32
		88  		exp += bias32
		89  	}
		90  	return
		91  }
		92  
		93  func fpack64(sign, mant uint64, exp int, trunc uint64) uint64 {
		94  	mant0, exp0, trunc0 := mant, exp, trunc
		95  	if mant == 0 {
		96  		return sign
		97  	}
		98  	for mant < 1<<mantbits64 {
		99  		mant <<= 1
	 100  		exp--
	 101  	}
	 102  	for mant >= 4<<mantbits64 {
	 103  		trunc |= mant & 1
	 104  		mant >>= 1
	 105  		exp++
	 106  	}
	 107  	if mant >= 2<<mantbits64 {
	 108  		if mant&1 != 0 && (trunc != 0 || mant&2 != 0) {
	 109  			mant++
	 110  			if mant >= 4<<mantbits64 {
	 111  				mant >>= 1
	 112  				exp++
	 113  			}
	 114  		}
	 115  		mant >>= 1
	 116  		exp++
	 117  	}
	 118  	if exp >= 1<<expbits64-1+bias64 {
	 119  		return sign ^ inf64
	 120  	}
	 121  	if exp < bias64+1 {
	 122  		if exp < bias64-int(mantbits64) {
	 123  			return sign | 0
	 124  		}
	 125  		// repeat expecting denormal
	 126  		mant, exp, trunc = mant0, exp0, trunc0
	 127  		for exp < bias64 {
	 128  			trunc |= mant & 1
	 129  			mant >>= 1
	 130  			exp++
	 131  		}
	 132  		if mant&1 != 0 && (trunc != 0 || mant&2 != 0) {
	 133  			mant++
	 134  		}
	 135  		mant >>= 1
	 136  		exp++
	 137  		if mant < 1<<mantbits64 {
	 138  			return sign | mant
	 139  		}
	 140  	}
	 141  	return sign | uint64(exp-bias64)<<mantbits64 | mant&(1<<mantbits64-1)
	 142  }
	 143  
	 144  func fpack32(sign, mant uint32, exp int, trunc uint32) uint32 {
	 145  	mant0, exp0, trunc0 := mant, exp, trunc
	 146  	if mant == 0 {
	 147  		return sign
	 148  	}
	 149  	for mant < 1<<mantbits32 {
	 150  		mant <<= 1
	 151  		exp--
	 152  	}
	 153  	for mant >= 4<<mantbits32 {
	 154  		trunc |= mant & 1
	 155  		mant >>= 1
	 156  		exp++
	 157  	}
	 158  	if mant >= 2<<mantbits32 {
	 159  		if mant&1 != 0 && (trunc != 0 || mant&2 != 0) {
	 160  			mant++
	 161  			if mant >= 4<<mantbits32 {
	 162  				mant >>= 1
	 163  				exp++
	 164  			}
	 165  		}
	 166  		mant >>= 1
	 167  		exp++
	 168  	}
	 169  	if exp >= 1<<expbits32-1+bias32 {
	 170  		return sign ^ inf32
	 171  	}
	 172  	if exp < bias32+1 {
	 173  		if exp < bias32-int(mantbits32) {
	 174  			return sign | 0
	 175  		}
	 176  		// repeat expecting denormal
	 177  		mant, exp, trunc = mant0, exp0, trunc0
	 178  		for exp < bias32 {
	 179  			trunc |= mant & 1
	 180  			mant >>= 1
	 181  			exp++
	 182  		}
	 183  		if mant&1 != 0 && (trunc != 0 || mant&2 != 0) {
	 184  			mant++
	 185  		}
	 186  		mant >>= 1
	 187  		exp++
	 188  		if mant < 1<<mantbits32 {
	 189  			return sign | mant
	 190  		}
	 191  	}
	 192  	return sign | uint32(exp-bias32)<<mantbits32 | mant&(1<<mantbits32-1)
	 193  }
	 194  
	 195  func fadd64(f, g uint64) uint64 {
	 196  	fs, fm, fe, fi, fn := funpack64(f)
	 197  	gs, gm, ge, gi, gn := funpack64(g)
	 198  
	 199  	// Special cases.
	 200  	switch {
	 201  	case fn || gn: // NaN + x or x + NaN = NaN
	 202  		return nan64
	 203  
	 204  	case fi && gi && fs != gs: // +Inf + -Inf or -Inf + +Inf = NaN
	 205  		return nan64
	 206  
	 207  	case fi: // ±Inf + g = ±Inf
	 208  		return f
	 209  
	 210  	case gi: // f + ±Inf = ±Inf
	 211  		return g
	 212  
	 213  	case fm == 0 && gm == 0 && fs != 0 && gs != 0: // -0 + -0 = -0
	 214  		return f
	 215  
	 216  	case fm == 0: // 0 + g = g but 0 + -0 = +0
	 217  		if gm == 0 {
	 218  			g ^= gs
	 219  		}
	 220  		return g
	 221  
	 222  	case gm == 0: // f + 0 = f
	 223  		return f
	 224  
	 225  	}
	 226  
	 227  	if fe < ge || fe == ge && fm < gm {
	 228  		f, g, fs, fm, fe, gs, gm, ge = g, f, gs, gm, ge, fs, fm, fe
	 229  	}
	 230  
	 231  	shift := uint(fe - ge)
	 232  	fm <<= 2
	 233  	gm <<= 2
	 234  	trunc := gm & (1<<shift - 1)
	 235  	gm >>= shift
	 236  	if fs == gs {
	 237  		fm += gm
	 238  	} else {
	 239  		fm -= gm
	 240  		if trunc != 0 {
	 241  			fm--
	 242  		}
	 243  	}
	 244  	if fm == 0 {
	 245  		fs = 0
	 246  	}
	 247  	return fpack64(fs, fm, fe-2, trunc)
	 248  }
	 249  
	 250  func fsub64(f, g uint64) uint64 {
	 251  	return fadd64(f, fneg64(g))
	 252  }
	 253  
	 254  func fneg64(f uint64) uint64 {
	 255  	return f ^ (1 << (mantbits64 + expbits64))
	 256  }
	 257  
	 258  func fmul64(f, g uint64) uint64 {
	 259  	fs, fm, fe, fi, fn := funpack64(f)
	 260  	gs, gm, ge, gi, gn := funpack64(g)
	 261  
	 262  	// Special cases.
	 263  	switch {
	 264  	case fn || gn: // NaN * g or f * NaN = NaN
	 265  		return nan64
	 266  
	 267  	case fi && gi: // Inf * Inf = Inf (with sign adjusted)
	 268  		return f ^ gs
	 269  
	 270  	case fi && gm == 0, fm == 0 && gi: // 0 * Inf = Inf * 0 = NaN
	 271  		return nan64
	 272  
	 273  	case fm == 0: // 0 * x = 0 (with sign adjusted)
	 274  		return f ^ gs
	 275  
	 276  	case gm == 0: // x * 0 = 0 (with sign adjusted)
	 277  		return g ^ fs
	 278  	}
	 279  
	 280  	// 53-bit * 53-bit = 107- or 108-bit
	 281  	lo, hi := mullu(fm, gm)
	 282  	shift := mantbits64 - 1
	 283  	trunc := lo & (1<<shift - 1)
	 284  	mant := hi<<(64-shift) | lo>>shift
	 285  	return fpack64(fs^gs, mant, fe+ge-1, trunc)
	 286  }
	 287  
	 288  func fdiv64(f, g uint64) uint64 {
	 289  	fs, fm, fe, fi, fn := funpack64(f)
	 290  	gs, gm, ge, gi, gn := funpack64(g)
	 291  
	 292  	// Special cases.
	 293  	switch {
	 294  	case fn || gn: // NaN / g = f / NaN = NaN
	 295  		return nan64
	 296  
	 297  	case fi && gi: // ±Inf / ±Inf = NaN
	 298  		return nan64
	 299  
	 300  	case !fi && !gi && fm == 0 && gm == 0: // 0 / 0 = NaN
	 301  		return nan64
	 302  
	 303  	case fi, !gi && gm == 0: // Inf / g = f / 0 = Inf
	 304  		return fs ^ gs ^ inf64
	 305  
	 306  	case gi, fm == 0: // f / Inf = 0 / g = Inf
	 307  		return fs ^ gs ^ 0
	 308  	}
	 309  	_, _, _, _ = fi, fn, gi, gn
	 310  
	 311  	// 53-bit<<54 / 53-bit = 53- or 54-bit.
	 312  	shift := mantbits64 + 2
	 313  	q, r := divlu(fm>>(64-shift), fm<<shift, gm)
	 314  	return fpack64(fs^gs, q, fe-ge-2, r)
	 315  }
	 316  
	 317  func f64to32(f uint64) uint32 {
	 318  	fs, fm, fe, fi, fn := funpack64(f)
	 319  	if fn {
	 320  		return nan32
	 321  	}
	 322  	fs32 := uint32(fs >> 32)
	 323  	if fi {
	 324  		return fs32 ^ inf32
	 325  	}
	 326  	const d = mantbits64 - mantbits32 - 1
	 327  	return fpack32(fs32, uint32(fm>>d), fe-1, uint32(fm&(1<<d-1)))
	 328  }
	 329  
	 330  func f32to64(f uint32) uint64 {
	 331  	const d = mantbits64 - mantbits32
	 332  	fs, fm, fe, fi, fn := funpack32(f)
	 333  	if fn {
	 334  		return nan64
	 335  	}
	 336  	fs64 := uint64(fs) << 32
	 337  	if fi {
	 338  		return fs64 ^ inf64
	 339  	}
	 340  	return fpack64(fs64, uint64(fm)<<d, fe, 0)
	 341  }
	 342  
	 343  func fcmp64(f, g uint64) (cmp int32, isnan bool) {
	 344  	fs, fm, _, fi, fn := funpack64(f)
	 345  	gs, gm, _, gi, gn := funpack64(g)
	 346  
	 347  	switch {
	 348  	case fn, gn: // flag NaN
	 349  		return 0, true
	 350  
	 351  	case !fi && !gi && fm == 0 && gm == 0: // ±0 == ±0
	 352  		return 0, false
	 353  
	 354  	case fs > gs: // f < 0, g > 0
	 355  		return -1, false
	 356  
	 357  	case fs < gs: // f > 0, g < 0
	 358  		return +1, false
	 359  
	 360  	// Same sign, not NaN.
	 361  	// Can compare encodings directly now.
	 362  	// Reverse for sign.
	 363  	case fs == 0 && f < g, fs != 0 && f > g:
	 364  		return -1, false
	 365  
	 366  	case fs == 0 && f > g, fs != 0 && f < g:
	 367  		return +1, false
	 368  	}
	 369  
	 370  	// f == g
	 371  	return 0, false
	 372  }
	 373  
	 374  func f64toint(f uint64) (val int64, ok bool) {
	 375  	fs, fm, fe, fi, fn := funpack64(f)
	 376  
	 377  	switch {
	 378  	case fi, fn: // NaN
	 379  		return 0, false
	 380  
	 381  	case fe < -1: // f < 0.5
	 382  		return 0, false
	 383  
	 384  	case fe > 63: // f >= 2^63
	 385  		if fs != 0 && fm == 0 { // f == -2^63
	 386  			return -1 << 63, true
	 387  		}
	 388  		if fs != 0 {
	 389  			return 0, false
	 390  		}
	 391  		return 0, false
	 392  	}
	 393  
	 394  	for fe > int(mantbits64) {
	 395  		fe--
	 396  		fm <<= 1
	 397  	}
	 398  	for fe < int(mantbits64) {
	 399  		fe++
	 400  		fm >>= 1
	 401  	}
	 402  	val = int64(fm)
	 403  	if fs != 0 {
	 404  		val = -val
	 405  	}
	 406  	return val, true
	 407  }
	 408  
	 409  func fintto64(val int64) (f uint64) {
	 410  	fs := uint64(val) & (1 << 63)
	 411  	mant := uint64(val)
	 412  	if fs != 0 {
	 413  		mant = -mant
	 414  	}
	 415  	return fpack64(fs, mant, int(mantbits64), 0)
	 416  }
	 417  
	 418  // 64x64 -> 128 multiply.
	 419  // adapted from hacker's delight.
	 420  func mullu(u, v uint64) (lo, hi uint64) {
	 421  	const (
	 422  		s		= 32
	 423  		mask = 1<<s - 1
	 424  	)
	 425  	u0 := u & mask
	 426  	u1 := u >> s
	 427  	v0 := v & mask
	 428  	v1 := v >> s
	 429  	w0 := u0 * v0
	 430  	t := u1*v0 + w0>>s
	 431  	w1 := t & mask
	 432  	w2 := t >> s
	 433  	w1 += u0 * v1
	 434  	return u * v, u1*v1 + w2 + w1>>s
	 435  }
	 436  
	 437  // 128/64 -> 64 quotient, 64 remainder.
	 438  // adapted from hacker's delight
	 439  func divlu(u1, u0, v uint64) (q, r uint64) {
	 440  	const b = 1 << 32
	 441  
	 442  	if u1 >= v {
	 443  		return 1<<64 - 1, 1<<64 - 1
	 444  	}
	 445  
	 446  	// s = nlz(v); v <<= s
	 447  	s := uint(0)
	 448  	for v&(1<<63) == 0 {
	 449  		s++
	 450  		v <<= 1
	 451  	}
	 452  
	 453  	vn1 := v >> 32
	 454  	vn0 := v & (1<<32 - 1)
	 455  	un32 := u1<<s | u0>>(64-s)
	 456  	un10 := u0 << s
	 457  	un1 := un10 >> 32
	 458  	un0 := un10 & (1<<32 - 1)
	 459  	q1 := un32 / vn1
	 460  	rhat := un32 - q1*vn1
	 461  
	 462  again1:
	 463  	if q1 >= b || q1*vn0 > b*rhat+un1 {
	 464  		q1--
	 465  		rhat += vn1
	 466  		if rhat < b {
	 467  			goto again1
	 468  		}
	 469  	}
	 470  
	 471  	un21 := un32*b + un1 - q1*v
	 472  	q0 := un21 / vn1
	 473  	rhat = un21 - q0*vn1
	 474  
	 475  again2:
	 476  	if q0 >= b || q0*vn0 > b*rhat+un0 {
	 477  		q0--
	 478  		rhat += vn1
	 479  		if rhat < b {
	 480  			goto again2
	 481  		}
	 482  	}
	 483  
	 484  	return q1*b + q0, (un21*b + un0 - q0*v) >> s
	 485  }
	 486  
	 487  func fadd32(x, y uint32) uint32 {
	 488  	return f64to32(fadd64(f32to64(x), f32to64(y)))
	 489  }
	 490  
	 491  func fmul32(x, y uint32) uint32 {
	 492  	return f64to32(fmul64(f32to64(x), f32to64(y)))
	 493  }
	 494  
	 495  func fdiv32(x, y uint32) uint32 {
	 496  	return f64to32(fdiv64(f32to64(x), f32to64(y)))
	 497  }
	 498  
	 499  func feq32(x, y uint32) bool {
	 500  	cmp, nan := fcmp64(f32to64(x), f32to64(y))
	 501  	return cmp == 0 && !nan
	 502  }
	 503  
	 504  func fgt32(x, y uint32) bool {
	 505  	cmp, nan := fcmp64(f32to64(x), f32to64(y))
	 506  	return cmp >= 1 && !nan
	 507  }
	 508  
	 509  func fge32(x, y uint32) bool {
	 510  	cmp, nan := fcmp64(f32to64(x), f32to64(y))
	 511  	return cmp >= 0 && !nan
	 512  }
	 513  
	 514  func feq64(x, y uint64) bool {
	 515  	cmp, nan := fcmp64(x, y)
	 516  	return cmp == 0 && !nan
	 517  }
	 518  
	 519  func fgt64(x, y uint64) bool {
	 520  	cmp, nan := fcmp64(x, y)
	 521  	return cmp >= 1 && !nan
	 522  }
	 523  
	 524  func fge64(x, y uint64) bool {
	 525  	cmp, nan := fcmp64(x, y)
	 526  	return cmp >= 0 && !nan
	 527  }
	 528  
	 529  func fint32to32(x int32) uint32 {
	 530  	return f64to32(fintto64(int64(x)))
	 531  }
	 532  
	 533  func fint32to64(x int32) uint64 {
	 534  	return fintto64(int64(x))
	 535  }
	 536  
	 537  func fint64to32(x int64) uint32 {
	 538  	return f64to32(fintto64(x))
	 539  }
	 540  
	 541  func fint64to64(x int64) uint64 {
	 542  	return fintto64(x)
	 543  }
	 544  
	 545  func f32toint32(x uint32) int32 {
	 546  	val, _ := f64toint(f32to64(x))
	 547  	return int32(val)
	 548  }
	 549  
	 550  func f32toint64(x uint32) int64 {
	 551  	val, _ := f64toint(f32to64(x))
	 552  	return val
	 553  }
	 554  
	 555  func f64toint32(x uint64) int32 {
	 556  	val, _ := f64toint(x)
	 557  	return int32(val)
	 558  }
	 559  
	 560  func f64toint64(x uint64) int64 {
	 561  	val, _ := f64toint(x)
	 562  	return val
	 563  }
	 564  
	 565  func f64touint64(x float64) uint64 {
	 566  	if x < float64(1<<63) {
	 567  		return uint64(int64(x))
	 568  	}
	 569  	y := x - float64(1<<63)
	 570  	z := uint64(int64(y))
	 571  	return z | (1 << 63)
	 572  }
	 573  
	 574  func f32touint64(x float32) uint64 {
	 575  	if x < float32(1<<63) {
	 576  		return uint64(int64(x))
	 577  	}
	 578  	y := x - float32(1<<63)
	 579  	z := uint64(int64(y))
	 580  	return z | (1 << 63)
	 581  }
	 582  
	 583  func fuint64to64(x uint64) float64 {
	 584  	if int64(x) >= 0 {
	 585  		return float64(int64(x))
	 586  	}
	 587  	// See ../cmd/compile/internal/gc/ssa.go:uint64Tofloat
	 588  	y := x & 1
	 589  	z := x >> 1
	 590  	z = z | y
	 591  	r := float64(int64(z))
	 592  	return r + r
	 593  }
	 594  
	 595  func fuint64to32(x uint64) float32 {
	 596  	return float32(fuint64to64(x))
	 597  }
	 598  

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