ref: b9656ec7e120d1fced20ea5ca826c57f2de4fc84
dir: /lib/std/fltfmt.myr/
use "alloc" use "bigint" use "die" use "extremum" use "fltbits" use "slpush" use "strbuf" use "types" use "utf" use "memops" pkg std = pkglocal const MNormal = 0 pkglocal const MAbsolute = 1 pkglocal const MRelative = 2 pkglocal const flt64bfmt : (sb : strbuf#, val : flt64, mode : int, precision : int -> void) pkglocal const flt32bfmt : (sb : strbuf#, val : flt32, mode : int, precision : int -> void) ;; const Dblbias = 1023 const Fltbias = 127 const flt64bfmt = {sb, val, mode, precision var isneg, exp, mant (isneg, exp, mant) = flt64explode(val) exp = max(exp, 1 - Dblbias) dragon4(sb, isneg, mant, exp - 52, Dblbias, mode, precision) } const flt32bfmt = {sb, val, mode, precision var isneg, exp, mant (isneg, exp, mant) = flt32explode(val) exp = (max((exp : int64), 1 - Fltbias) : int32) dragon4(sb, isneg, (mant : uint64), (exp - 23 : int64), Fltbias, mode, precision) } /* sb: output buffer e: exponent p: precision f: mantissa floating value: x = f^(e - p) */ const dragon4 = {sb, isneg, f, e, p, mode, cutoff var r, s, t, u, v, y var udig var mm, mp /* margins above and below */ var roundup var low, high var k var a, i if isneg sbputs(sb, "-") ;; /* if we have zero for the mantissa, we can return early */ if f == 0 sbputs(sb, "0.0") -> void ;; /* initialize */ roundup = false low = false high = false u = mkbigint(0) r = bigshli(mkbigint(f), max(e, 0)) s = bigshli(mkbigint(1), max(0, -e)) mm = bigshli(mkbigint(1), max(e, 0)) mp = bigdup(mm) /* fixup: unequal gaps */ t = mkbigint(1) bigshli(t, p - 1) if bigeqi(t, f) bigshli(mp, 1) bigshli(r, 1) bigshli(s, 1) ;; bigfree(t) k = 0 while true /* r < ceil(s/b) */ t = bigdup(s) bigaddi(t, 9) bigdivi(t, 10) match bigcmp(r, t) | `Before: k-- bigmuli(r, 10) bigmuli(mm, 10) bigmuli(mp, 10) | _: bigfree(t) break ;; bigfree(t) ;; while true t = bigdup(r) bigshli(t, 1) bigadd(t, mp) while true u = bigdup(s) bigshli(u, 1) match bigcmp(t, u) | `Before: bigfree(u) break | _: k++ bigmuli(s, 10) bigfree(u) ;; ;; if mode == MNormal cutoff = k else if mode == MRelative cutoff += k - 1 ;; /* common between relative and absolute */ a = cutoff - k - 1 y = bigdup(s) if a < 0 for i = 0; i < a; i++ bigmuli(y, 10) ;; else for i = 0; i < -a; i++ bigaddi(y, 9) bigdivi(y, 10) ;; ;; match bigcmp(y, mm) | `Before: /* nothing */ | _: bigfree(mm) mm = y ;; match bigcmp(y, mp) | `Before: /* nothing */ | _: bigfree(mp) mp = y roundup = true ;; ;; u = bigdup(s) bigshli(u, 1) match bigcmp(t, u) | `Before: bigfree(t) bigfree(u) break | _: ;; ;; if k <= 0 sbputs(sb, "0.") for var i = 0; i < -k; i++ sbputs(sb, "0") ;; ;; while true k-- bigmuli(r, 10) u = bigdup(r); bigdiv(u, s) bigmod(r, s) bigmuli(mm, 10) bigmuli(mp, 10) low = false t = bigdup(r) bigshli(t, 1) match bigcmp(t, mm) | `Before: low = true | _: ;; bigfree(t) /* v = 2*r */ v = bigdup(r) bigshli(v, 1) /* t = 2*s - mp */ t = bigdup(s) bigshli(t, 1) bigsub(t, mp) match bigcmp(v, t) | `Before: high = false; | `Equal: high = roundup; | `After: high = true; ;; bigfree(v) bigfree(t) if low || high || k == cutoff break ;; format(sb, lowdig(u), k) bigfree(u) ;; /* format the last digit */ udig = lowdig(u) if low && !high format(sb, udig, k) elif high && !low format(sb, udig + 1, k) else bigmuli(r, 2) match bigcmp(r, s) | `Before: format(sb, udig, k) | `Equal: format(sb, udig, k) | `After: format(sb, udig + 1, k) ;; ;; k-- while k >= -1 format(sb, 0, k--) ;; bigfree(u) bigfree(r) bigfree(s) bigfree(mm) bigfree(mp) } const lowdig = {u if u.dig.len > 0 -> u.dig[0] ;; -> 0 } const format = {sb, d, k const dig = "0123456789" sbputb(sb, dig[d]) if k == 0 sbputs(sb, ".") ;; }