ref: aa40abd25de6fc94621a41b360b5808b3aa57b55
dir: /lib/std/fltparse.myr/
use "alloc"
use "bigint"
use "chartype"
use "chomp"
use "extremum"
use "fltbits"
use "hasprefix"
use "intparse"
use "option"
use "utf"
use "striter"
pkg std =
const flt64parse : (str : byte[:] -> std.option(flt64))
const flt32parse : (str : byte[:] -> std.option(flt32))
;;
type parseresult = union
`Flt (int, std.bigint#, int16)
`Inf int
`Nan int
`Badflt
;;
const flt64parse = {str
var val
match fltparse(str)
| `Badflt: -> `std.None
| `Inf sign: -> `std.Some ((sign : flt64) * std.flt64inf())
| `Nan sign: -> `std.Some ((sign : flt64) * std.flt64nan())
| `Flt (sign, mant, exp):
val = toflt(sign, mant, exp, &lim64)
std.bigfree(mant)
-> `std.Some val
;;
}
const flt32parse = {str
var val
match fltparse(str)
| `Badflt: -> `std.None
| `Inf sign: -> `std.Some ((sign : flt32) * std.flt32inf())
| `Nan sign: -> `std.Some ((sign : flt32) * std.flt32nan())
| `Flt (sign, mant, exp):
val = toflt(sign, mant, exp, &lim32)
std.bigfree(mant)
-> `std.Some (val : flt32)
;;
}
const fltparse = {str
var sign, exp, mant, expinc, i
if std.chomp(&str, "-")
sign = -1
else
sign = 1
std.chomp(&str, "+")
;;
match str
| "inf": -> `Inf sign
| "Inf": -> `Inf sign
| "nan": -> `Nan sign
| "NaN": -> `Nan sign
| "": -> `Badflt
| _: /* nothing */
;;
i = 0
exp = 0
expinc = 0
mant = std.mkbigint(0)
for var c = std.decode(str[i:]); c == '0'; c = std.decode(str[i:])
i++
;;
for var c = std.decode(str[i:]); fltchar(c); c = std.decode(str[i:])
i++
if c == '_'
continue
elif c == '.'
/* fail if we've already seen the '.' */
if expinc != 0
goto error
;;
expinc = -1
elif std.isdigit(c)
exp += expinc
std.bigmuli(mant, 10)
std.bigaddi(mant, std.charval(c, 10))
else
goto error
;;
;;
if std.hasprefix(str[i:], "e") || std.hasprefix(str[i:], "E")
/* intparse doesn't accept '+', so if we have 'e+', consume the '+ */
if std.hasprefix(str[i+1:], "+")
i++
;;
match std.intparsebase(str[i+1:], 10)
| `std.Some n: exp += n
| `std.None: goto error
;;
i = str.len
;;
if i != str.len
goto error
;;
-> `Flt (sign, mant, exp)
:error
std.bigfree(mant)
-> `Badflt
}
const fltchar = {c
-> std.isdigit(c) || c == '.' || c == '_'
}
type lim = struct
minsig : uint64
maxsig : uint64
loshift : uint64
nextinc : int64
minexp : int16
maxexp : int16
sigbits : int16
;;
const lim64 : lim = [
.minsig=0x10000000000000ul,
.maxsig=0x20000000000000ul,
.minexp=-1022 - 52,
.maxexp=1023 - 52,
.sigbits=53,
.nextinc=1,
.loshift=0
]
const lim32 : lim = [
.minsig=0x400000,
.maxsig=0x800000,
.minexp=-126-22,
.maxexp=127-22,
.sigbits=22,
.nextinc=0x20000000,
.loshift=30
]
const toflt = {sign, mant, exp, lim
/* if it's all zero, just return 0 */
if std.bigeqi(mant, 0)
-> (sign : flt64) * 0.0
/* todo: add fast parsing for common cases */
else
-> (sign : flt64) * fallback(mant, exp, lim)
;;
}
const fallback = {mant, exp, lim
var u, v, k : int16, eabs
var x, r, xprime, rprime
var f
u = mant
k = 0
v = std.mkbigint(1)
x = std.mkbigint(0)
r = std.mkbigint(0)
eabs = std.abs(exp)
if exp >= 0
/* can be optimized */
mulexp(u, eabs, 10)
else
mulexp(v, eabs, 10)
;;
estimate(u, v, &k, lim)
while true
(xprime, rprime) = std.bigdivmod(u, v)
std.bigmove(x, xprime)
std.bigmove(r, rprime)
if k == lim.minexp
if std.biggei(x, lim.minsig) && std.biglei(x, lim.maxsig)
break
else
f = denormal(x, v, r, lim)
goto done
;;
elif k > lim.maxexp
-> std.flt64inf()
;;
if std.biglti(x, lim.minsig)
std.bigmuli(u, 2)
k--
elif std.biggti(x, lim.maxsig)
std.bigmuli(v, 2)
k++
else
break
;;
;;
f = assemble(u, v, r, k, lim)
:done
std.bigfree(v)
std.bigfree(x)
std.bigfree(r)
-> f
}
const estimate = {u, v, k, lim
var log2u, log2v, log2rat
var ushift, vshift
var targ
targ = lim.sigbits
log2u = std.bigbitcount(u)
log2v = std.bigbitcount(v)
ushift = 0
vshift = 0
log2rat = (log2u - log2v : int16)
/*
if we deal with denormals, we just punt to the 'k == minexp' test
and take the slow path.
*/
if log2rat < targ - 1
ushift = std.clamp(targ - log2rat - 1, lim.minexp, lim.maxexp)
k# -= ushift
elif log2rat > targ + 1
vshift = std.clamp(log2rat - targ + 1, lim.minexp, lim.maxexp)
k# += vshift
;;
std.bigshli(u, ushift)
std.bigshli(v, vshift)
}
const assemble = {u, v, r, k, lim
var z, diff
std.bigdiv(u, v)
diff = std.bigdup(v)
std.bigsub(diff, r)
z = mkflt(u, k)
match std.bigcmp(r, diff)
| `std.Before: /* nothing */
| `std.After: z = nextfloat(z, lim)
| `std.Equal:
if !std.bigiseven(u)
z = nextfloat(z, lim)
;;
;;
std.bigfree(diff)
-> z
}
const nextfloat = {z, lim
var sign, mant, exp
var za
(sign, mant, exp) = std.flt64explode(z)
if std.abs(mant - (1l << 52) - 1) < lim.nextinc
mant = 0
exp++
else
mant += lim.nextinc
;;
za = std.flt64assem(sign, mant, exp)
-> za
}
const mulexp = {val, exp, pow
while exp > 0
exp--
std.bigmuli(val, pow)
;;
}
const denormal = {x, v, rem, lim
var m, z
if x.dig.len == 0
m = 0
elif x.dig.len == 2
m = (x.dig[0] : uint64)
m |= (x.dig[1] : uint64) << 32
else
m = (x.dig[0] : uint64) << lim.loshift
;;
z = std.flt64frombits(m)
match std.bigcmp(rem, v)
| `std.Before: /* nothing */
| `std.After: z = nextfloat(z, lim)
| `std.Equal:
if !std.bigiseven(x)
z = nextfloat(z, lim)
;;
;;
-> z
}
const mkflt = {mant, exp
var m, e
if mant.dig.len == 2
/* flt64: guaranteed to be in the range 2^52..2^53 */
m = (mant.dig[0] : uint64)
m |= (mant.dig[1] : uint64) << 32
else
/* flt32: 2^22..2^23, so adjust into flt64 range */
m = (mant.dig[0] : uint64) << 30
exp -= 30
;;
m &= (1<<52) - 1
e = (exp : uint64)
e += 1023 + 52 /* exponent bias */
e &= 0x7ff
e <<= 52
-> std.flt64frombits(m | e)
}