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usr/apps/calc.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <unistd.h>
+#include <cervus_util.h>
+
+#define SCALE   1000000LL
+
+typedef long long fx;
+
+static const char *p;
+
+static void skip_ws(void) { while (*p && isspace((unsigned char)*p)) p++; }
+
+static fx parse_number(int *err)
+{
+    skip_ws();
+    long long intpart = 0, frac = 0, fscale = 1;
+    int had_digit = 0;
+    while (isdigit((unsigned char)*p)) {
+        intpart = intpart * 10 + (*p - '0');
+        had_digit = 1; p++;
+    }
+    if (*p == '.') {
+        p++;
+        while (isdigit((unsigned char)*p)) {
+            if (fscale < SCALE) { frac = frac * 10 + (*p - '0'); fscale *= 10; }
+            had_digit = 1; p++;
+        }
+    }
+    if (!had_digit) { *err = 1; return 0; }
+    return intpart * SCALE + (frac * SCALE) / fscale;
+}
+
+static fx parse_expr(int *err);
+
+static fx parse_primary(int *err)
+{
+    skip_ws();
+    if (*p == '(') {
+        p++;
+        fx v = parse_expr(err);
+        skip_ws();
+        if (*p == ')') p++;
+        else           *err = 1;
+        return v;
+    }
+    if (*p == '-') { p++; return -parse_primary(err); }
+    if (*p == '+') { p++; return  parse_primary(err); }
+    return parse_number(err);
+}
+
+static fx parse_term(int *err)
+{
+    fx v = parse_primary(err);
+    while (!*err) {
+        skip_ws();
+        if (*p == '*') {
+            p++;
+            fx r = parse_primary(err);
+            v = (v * r) / SCALE;
+        } else if (*p == '/') {
+            p++;
+            fx r = parse_primary(err);
+            if (r == 0) { *err = 2; return 0; }
+            v = (v * SCALE) / r;
+        } else break;
+    }
+    return v;
+}
+
+static fx parse_expr(int *err)
+{
+    fx v = parse_term(err);
+    while (!*err) {
+        skip_ws();
+        if (*p == '+') { p++; v += parse_term(err); }
+        else if (*p == '-') { p++; v -= parse_term(err); }
+        else break;
+    }
+    return v;
+}
+
+static void print_fx(fx v)
+{
+    if (v < 0) { putchar('-'); v = -v; }
+    long long ip = v / SCALE;
+    long long fp = v % SCALE;
+
+    char ibuf[32];
+    int ilen = 0;
+    if (ip == 0) {
+        ibuf[ilen++] = '0';
+    } else {
+        long long tmp = ip;
+        while (tmp > 0) { ibuf[ilen++] = '0' + (int)(tmp % 10); tmp /= 10; }
+        for (int a = 0, b = ilen - 1; a < b; a++, b--) {
+            char t = ibuf[a]; ibuf[a] = ibuf[b]; ibuf[b] = t;
+        }
+    }
+    ibuf[ilen] = '\0';
+    fputs(ibuf, stdout);
+
+    if (fp != 0) {
+        char fbuf[8];
+        int flen = 0;
+        long long tmp = fp;
+        long long scale = SCALE;
+        fbuf[flen++] = '.';
+        while (scale > 1) {
+            scale /= 10;
+            fbuf[flen++] = '0' + (int)(tmp / scale);
+            tmp %= scale;
+        }
+        fbuf[flen] = '\0';
+        while (flen > 1 && fbuf[flen - 1] == '0') { fbuf[--flen] = '\0'; }
+        fputs(fbuf, stdout);
+    }
+    putchar('\n');
+}
+
+static void calc_help(void)
+{
+    putchar('\n');
+    fputs(C_CYAN "Cervus calc" C_RESET " - fixed-point calculator (6 decimal digits)\n", stdout);
+    fputs(C_GRAY "-------------------------------------------" C_RESET "\n", stdout);
+    fputs(C_BOLD "Operators:" C_RESET "  +  -  *  /  ( )\n", stdout);
+    fputs(C_GRAY "-------------------------------------------" C_RESET "\n", stdout);
+    fputs(C_BOLD "Examples:" C_RESET "\n", stdout);
+    fputs("  calc> " C_YELLOW "3.14 + 5" C_RESET "        = 8.14\n", stdout);
+    fputs("  calc> " C_YELLOW "10 / 3" C_RESET "          = 3.333333\n", stdout);
+    fputs("  calc> " C_YELLOW "2 * (3 + 4)" C_RESET "     = 14\n", stdout);
+    fputs("  calc> " C_YELLOW "(1.5 + 2.5) * 4" C_RESET " = 16\n", stdout);
+    fputs("  calc> " C_YELLOW "100 / 7" C_RESET "         = 14.285714\n", stdout);
+    fputs("  calc> " C_YELLOW "-5 + 3" C_RESET "          = -2\n", stdout);
+    fputs(C_GRAY "-------------------------------------------" C_RESET "\n", stdout);
+    fputs("  Type " C_BOLD "q" C_RESET " or " C_BOLD "exit" C_RESET " to quit.\n", stdout);
+    putchar('\n');
+}
+
+static int readline_calc(char *buf, int maxlen)
+{
+    int i = 0;
+    for (;;) {
+        char c;
+        ssize_t r = read(0, &c, 1);
+        if (r <= 0) {
+            buf[i] = '\0';
+            return (i > 0) ? i : -1;
+        }
+        if (c == '\r') continue;
+        if (c == '\n') {
+            write(1, "\n", 1);
+            buf[i] = '\0';
+            return i;
+        }
+        if (c == '\b' || c == 0x7F) {
+            if (i > 0) {
+                i--;
+                write(1, "\b \b", 3);
+            }
+            continue;
+        }
+        if (c == 0x03) {
+            write(1, "^C\n", 3);
+            buf[0] = '\0';
+            return 0;
+        }
+        if (c >= 0x20 && c < 0x7F && i < maxlen - 1) {
+            buf[i++] = c;
+            write(1, &c, 1);
+        }
+    }
+}
+
+int main(int argc, char **argv)
+{
+    (void)argc; (void)argv;
+    fputs(C_CYAN "Cervus calc" C_RESET " - fixed-point (6 digits). "
+          "Type " C_BOLD "help" C_RESET " for examples, " C_BOLD "q" C_RESET " to exit.\n", stdout);
+
+    char line[256];
+    for (;;) {
+        fputs("calc> ", stdout);
+        int n = readline_calc(line, sizeof(line));
+        if (n < 0) { putchar('\n'); break; }
+        while (n > 0 && isspace((unsigned char)line[n - 1])) line[--n] = '\0';
+        if (n == 0) continue;
+        if (strcmp(line, "q") == 0 || strcmp(line, "quit") == 0 ||
+            strcmp(line, "exit") == 0) break;
+        if (strcmp(line, "help") == 0) { calc_help(); continue; }
+
+        p = line;
+        int err = 0;
+        fx v = parse_expr(&err);
+        skip_ws();
+        if (*p != '\0') err = 1;
+
+        if (err == 1)       fputs(C_RED "  parse error\n" C_RESET, stdout);
+        else if (err == 2)  fputs(C_RED "  division by zero\n" C_RESET, stdout);
+        else { fputs("  = ", stdout); print_fx(v); }
+    }
+    putchar('\n');
+    return 0;
+}