90 lines
1.9 KiB
C
90 lines
1.9 KiB
C
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#include <math.h>
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#include <float.h>
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#include <iso646.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <stdio.h>
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size_t f(float x, int n)
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{
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bool is_negative = x < 0;
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x = fabsf(x);
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float pow10 = 1;
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float factor = n < 0 ? 0.1 : 10;
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size_t decs = 0;
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size_t zeroes = 0;
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for (int i = 0; decs < FLT_DIG and i < abs(n); i++) {
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float next_pow = pow10 * factor;
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float mod = fmodf(x * next_pow, 10);
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if (mod == 0)
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break;
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pow10 = next_pow;
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if (decs != 0 or (int)mod != 0)
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decs += 1;
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else
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zeroes += 1;
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}
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decs += n * (n < 0);
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uint_fast64_t x_integ = roundf(x * pow10);
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size_t ints = 0;
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for (int y = x_integ / pow10; y > 0; y /= 10)
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ints += 1;
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size_t len = (is_negative) + (ints == 0) + ints + (decs != 0) + zeroes + decs;
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char buf[len + 1];
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buf[len] = 0;
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for (int i = 0; i < decs; i++) {
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buf[--len] = x_integ % 10 + 48;
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x_integ /= 10;
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}
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for (int i = 0; i < zeroes; i++) {
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buf[--len] = '0';
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}
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if (decs != 0)
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buf[--len] = '.';
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if (n < 0) for (int i = 0; i < -n; i++) {
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buf[--len] = '0';
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}
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if (ints == 0) {
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buf[--len] = '0';
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} else for (int i = 0; i < ints; i++) {
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buf[--len] = x_integ % 10 + 48;
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x_integ /= 10;
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}
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if (is_negative)
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buf[--len] = '-';
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printf("%s\n", buf);
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printf("\t%f : decs:%llu, ints:%u, zeroes:%u\n", pow10, decs, ints, zeroes);
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}
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int main()
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{
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f(39, 3); // "39"
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f(39.39, 9); // "39.39"
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f(0.3939, 3); // "0.394"
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f(39e-9, 9); // "0.000000039"
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f(3939, -2); // "3900"
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f(39.99, 0); // 39.99 expected: 40
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f(39.99, 1); // 39. expected: 40
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f(39.99, 2); // 39. expected: 39.99
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f(-39.3939, 3); // -39.4 expected: -39.394
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return 0;
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}
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