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  1. #include <stdio.h>
  2. #include <math.h>
  3. #include <string.h>
  4. #include <stdint.h>
  5.  
  6. char *fmtp04f(char *buf, char *lim, double d) {
  7.     // if there's no space at all don't bother
  8.     if(buf==lim) return buf;
  9.     // 10 characters in maximum 32 bit integer, one for the dot,
  10.     // one for the terminating NUL in debug prints
  11.     char b[12];
  12.     // current position in the buffer
  13.     char *bp = b;
  14.     // scale and round
  15.     int32_t i = lrint(d * 10000.);
  16.     // write sign and fix i sign
  17.     // (we do have at least one character available in buf)
  18.     if(signbit(d)) {
  19.         *buf++='-';
  20.         i = -i;
  21.     } else {
  22.         *buf++='+';
  23.     }
  24.     // *always* write down the last 4 digits, even if they are zeroes
  25.     // (they'll become the 4 digits after the decimal dot)
  26.     for(; bp!=b+4; ) {
  27.         *bp++ = '0' + i%10;
  28.         i/=10;
  29.     }
  30.     *bp++='.';
  31.     // write down the remaining digits, writing at least one
  32.     do {
  33.         *bp++ = '0' + i%10;
  34.         i/=10;
  35.     } while(i != 0);
  36.     // bp is at the character after the last, step back
  37.     --bp;
  38.     // data is now into b *in reversed order*;
  39.     // reverse-copy it into the user-provided buffer
  40.     while(buf!=lim) {
  41.         *buf++ = *bp;
  42.         // check before decrementing, as a pointer to one-before-first
  43.         // is not allowed in C
  44.         if(bp == b) break;
  45.         --bp;
  46.     }
  47.     if(buf!=lim) *buf=0;    // "regular" case: terminate *after*
  48.     else         lim[-1]=0; // bad case: truncate
  49.     return buf;
  50. }
  51.  
  52. void doformat(char *buf, char *lim, double a, double b) {
  53.     if(buf==lim) return; // cannot do anything
  54.     *buf++='{';
  55.     if(buf==lim) goto end;
  56.     buf = fmtp04f(buf, lim, a);
  57.     if(buf==lim) return; // already terminated by fmtp04f
  58.     *buf++=',';
  59.     if(buf==lim) goto end;
  60.     buf = fmtp04f(buf, lim, b);
  61.     if(buf==lim) return; // idem
  62.     *buf++='}';
  63.     if(buf==lim) goto end;
  64.     *buf++=0;
  65. end:
  66.     lim[-1]=0;   // always terminate
  67. }
  68.  
  69. int main() {
  70.     double test_cases[] = {0., 1., 100., 1.2345678, 12345.678, 3.1415, 9.115251, 99999.1234, 0.};
  71.     char buf1[22];
  72.     char buf2[256];
  73.     char *buf2r = buf2+128;
  74.     for(int i=0, n=(sizeof(test_cases)/sizeof(*test_cases))-1; i<n; ++i) {
  75.         for(int sgn = 0; sgn<4; ++sgn) {
  76.             memset(buf2, 255, sizeof(buf2));
  77.             double a = test_cases[i];
  78.             if(sgn&1) a = -a;
  79.             double b = test_cases[i+1];
  80.             if(sgn&2) b = -b;
  81.             snprintf(buf1, sizeof(buf1), "{%+0.4f,%+0.4f}", a, b);
  82.             puts(buf1);
  83.             doformat(buf2r, buf2r+22, a, b);
  84.             puts(buf2r);
  85.             if(strcmp(buf2r, buf1)) {
  86.                 printf("buf1 [%s] != buf2r [%s]\n", buf1, buf2r);
  87.             }
  88.             for(const char *p=buf2; p<buf2r; ++p) {
  89.                 if((unsigned char)(*p)!=255) {
  90.                     printf("unexpected %d at %d\n", *p, (int)(p-buf2));
  91.                 }
  92.             }
  93.             for(const char *p=buf2r+22; p<buf2 + sizeof(buf2); ++p) {
  94.                 if((unsigned char)(*p)!=255) {
  95.                     printf("unexpected %d at %d\n", *p, (int)(p-buf2));
  96.                 }
  97.             }
  98.         }
  99.     }
  100.     return 0;
  101.  
  102. }
  103.  
Success #stdin #stdout 0s 9432KB
comments (?)
stdin
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Standard input is empty
stdout
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{+0.0000,+1.0000}
{+0.0000,+1.0000}
{-0.0000,+1.0000}
{-0.0000,+1.0000}
{+0.0000,-1.0000}
{+0.0000,-1.0000}
{-0.0000,-1.0000}
{-0.0000,-1.0000}
{+1.0000,+100.0000}
{+1.0000,+100.0000}
{-1.0000,+100.0000}
{-1.0000,+100.0000}
{+1.0000,-100.0000}
{+1.0000,-100.0000}
{-1.0000,-100.0000}
{-1.0000,-100.0000}
{+100.0000,+1.2346}
{+100.0000,+1.2346}
{-100.0000,+1.2346}
{-100.0000,+1.2346}
{+100.0000,-1.2346}
{+100.0000,-1.2346}
{-100.0000,-1.2346}
{-100.0000,-1.2346}
{+1.2346,+12345.6780}
{+1.2346,+12345.6780}
{-1.2346,+12345.6780}
{-1.2346,+12345.6780}
{+1.2346,-12345.6780}
{+1.2346,-12345.6780}
{-1.2346,-12345.6780}
{-1.2346,-12345.6780}
{+12345.6780,+3.1415}
{+12345.6780,+3.1415}
{-12345.6780,+3.1415}
{-12345.6780,+3.1415}
{+12345.6780,-3.1415}
{+12345.6780,-3.1415}
{-12345.6780,-3.1415}
{-12345.6780,-3.1415}
{+3.1415,+9.1153}
{+3.1415,+9.1153}
{-3.1415,+9.1153}
{-3.1415,+9.1153}
{+3.1415,-9.1153}
{+3.1415,-9.1153}
{-3.1415,-9.1153}
{-3.1415,-9.1153}
{+9.1153,+99999.1234}
{+9.1153,+99999.1234}
{-9.1153,+99999.1234}
{-9.1153,+99999.1234}
{+9.1153,-99999.1234}
{+9.1153,-99999.1234}
{-9.1153,-99999.1234}
{-9.1153,-99999.1234}
{+99999.1234,+0.0000}
{+99999.1234,+0.0000}
{-99999.1234,+0.0000}
{-99999.1234,+0.0000}
{+99999.1234,-0.0000}
{+99999.1234,-0.0000}
{-99999.1234,-0.0000}
{-99999.1234,-0.0000}
https://ideone.com/w0RUjR
language:
C (gcc 8.3)
created:
8 years ago
visibility:
public

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