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* The authors of this software are Rob Pike and Ken Thompson.
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* Copyright (c) 2002 by Lucent Technologies.
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* Permission to use, copy, modify, and distribute this software for any
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* purpose without fee is hereby granted, provided that this entire notice
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* is included in all copies of any software which is or includes a copy
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* or modification of this software and in all copies of the supporting
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* documentation for such software.
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* THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
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* WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE
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* ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
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* OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
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* first few powers of 10, enough for about 1/2 of the
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* total space for doubles.
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static double pows10[] =
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1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
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1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
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1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29,
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1e30, 1e31, 1e32, 1e33, 1e34, 1e35, 1e36, 1e37, 1e38, 1e39,
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1e40, 1e41, 1e42, 1e43, 1e44, 1e45, 1e46, 1e47, 1e48, 1e49,
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1e50, 1e51, 1e52, 1e53, 1e54, 1e55, 1e56, 1e57, 1e58, 1e59,
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1e60, 1e61, 1e62, 1e63, 1e64, 1e65, 1e66, 1e67, 1e68, 1e69,
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1e70, 1e71, 1e72, 1e73, 1e74, 1e75, 1e76, 1e77, 1e78, 1e79,
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1e80, 1e81, 1e82, 1e83, 1e84, 1e85, 1e86, 1e87, 1e88, 1e89,
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1e90, 1e91, 1e92, 1e93, 1e94, 1e95, 1e96, 1e97, 1e98, 1e99,
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1e100, 1e101, 1e102, 1e103, 1e104, 1e105, 1e106, 1e107, 1e108, 1e109,
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1e110, 1e111, 1e112, 1e113, 1e114, 1e115, 1e116, 1e117, 1e118, 1e119,
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1e120, 1e121, 1e122, 1e123, 1e124, 1e125, 1e126, 1e127, 1e128, 1e129,
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1e130, 1e131, 1e132, 1e133, 1e134, 1e135, 1e136, 1e137, 1e138, 1e139,
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1e140, 1e141, 1e142, 1e143, 1e144, 1e145, 1e146, 1e147, 1e148, 1e149,
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1e150, 1e151, 1e152, 1e153, 1e154, 1e155, 1e156, 1e157, 1e158, 1e159,
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#define pow10(x) fmtpow10(x)
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if(n < DBL_MIN_10_EXP){
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}else if(n > DBL_MAX_10_EXP){
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if(n < (int)(sizeof(pows10)/sizeof(pows10[0])))
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d = pows10[sizeof(pows10)/sizeof(pows10[0]) - 1];
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n -= sizeof(pows10)/sizeof(pows10[0]) - 1;
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if(n < (int)(sizeof(pows10)/sizeof(pows10[0]))){
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d *= pows10[sizeof(pows10)/sizeof(pows10[0]) - 1];
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xadd(char *a, int n, int v)
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if(n < 0 || n >= NSIGNIF)
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for(b = a+n; b >= a; b--) {
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*a = '1'; /* overflow adding */
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xsub(char *a, int n, int v)
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for(b = a+n; b >= a; b--) {
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*a = '9'; /* underflow subtracting */
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xdtoa(Fmt *fmt, char *s2, double f)
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int c1, c2, c3, c4, ucase, sign, chr, prec;
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if(fmt->flags & FmtPrec)
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e = e * .301029995664;
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if(e >= -150 && e <= +150) {
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* convert NSIGNIF digits and convert
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* back to get accuracy.
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for(i=0; i<NSIGNIF; i++) {
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* try decimal rounding to eliminate 9s
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if(c2 >= NSIGNIF-2) {
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sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
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if(xadd(s1, NSIGNIF-3, 1)) {
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sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
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* convert back so s1 gets exact answer
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sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
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if(xadd(s1, NSIGNIF-1, 1))
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if(xsub(s1, NSIGNIF-1, 1))
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else if(fmt->flags & FmtSign)
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else if(fmt->flags & FmtSpace)
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* copy into final place
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* c1 digits of leading '0'
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* c2 digits from conversion
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* c3 digits of trailing '0'
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* c4 digits after '.'
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* decide on 'e' of 'f' style convers
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if(e >= -5 && e <= prec) {
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chr = 'h'; // flag for 'f' style
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if(xadd(s1, c2+e, 5))
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* clean up c1 c2 and c3
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* strip trailing '0' on g conv
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if(fmt->flags & FmtSharp) {
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if(chr == 'g' || chr == 'h') {
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for(n=d-1; n>=0; n--)
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if(chr == 'e' || chr == 'g') {
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s2[d++] = c1/100 + '0';
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s2[d++] = c1/10 + '0';
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s2[d++] = c1%10 + '0';
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floatfmt(Fmt *fmt, double f)
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fmt->flags &= FmtWidth|FmtLeft;
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__fmtcpy(fmt, s, strlen(s), strlen(s));
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d = va_arg(f->args, double);
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return floatfmt(f, d);