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usr/lib/libcervus/stdlib/strtod.c

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+#include <stdint.h>
+#include <stddef.h>
+
+uint64_t __cervus_strtod_bits(const char *s, char **endptr)
+{
+    if (!s) {
+        if (endptr) *endptr = (char *)s;
+        return 0;
+    }
+    const char *p = s;
+    while (*p == ' ' || *p == '\t' || *p == '\n' ||
+           *p == '\r' || *p == '\f' || *p == '\v') p++;
+
+    int sign = 0;
+    if (*p == '+') p++;
+    else if (*p == '-') { sign = 1; p++; }
+
+    if ((p[0] == 'i' || p[0] == 'I') &&
+        (p[1] == 'n' || p[1] == 'N') &&
+        (p[2] == 'f' || p[2] == 'F')) {
+        p += 3;
+        if ((p[0] == 'i' || p[0] == 'I') &&
+            (p[1] == 'n' || p[1] == 'N') &&
+            (p[2] == 'i' || p[2] == 'I') &&
+            (p[3] == 't' || p[3] == 'T') &&
+            (p[4] == 'y' || p[4] == 'Y')) p += 5;
+        if (endptr) *endptr = (char *)p;
+        return ((uint64_t)sign << 63) | 0x7FF0000000000000ULL;
+    }
+    if ((p[0] == 'n' || p[0] == 'N') &&
+        (p[1] == 'a' || p[1] == 'A') &&
+        (p[2] == 'n' || p[2] == 'N')) {
+        p += 3;
+        if (endptr) *endptr = (char *)p;
+        return 0x7FF8000000000000ULL;
+    }
+
+    uint64_t mant    = 0;
+    int      dec_exp = 0;
+    int      seen_digit = 0;
+
+    while (*p >= '0' && *p <= '9') {
+        seen_digit = 1;
+        if (mant <= (UINT64_MAX - 9) / 10) {
+            mant = mant * 10 + (uint64_t)(*p - '0');
+        } else {
+            dec_exp++;
+        }
+        p++;
+    }
+    if (*p == '.') {
+        p++;
+        while (*p >= '0' && *p <= '9') {
+            seen_digit = 1;
+            if (mant <= (UINT64_MAX - 9) / 10) {
+                mant = mant * 10 + (uint64_t)(*p - '0');
+                dec_exp--;
+            }
+            p++;
+        }
+    }
+    if (!seen_digit) {
+        if (endptr) *endptr = (char *)s;
+        return 0;
+    }
+
+    if (*p == 'e' || *p == 'E') {
+        const char *ep = p + 1;
+        int esign = 0;
+        if (*ep == '+') ep++;
+        else if (*ep == '-') { esign = 1; ep++; }
+        if (*ep >= '0' && *ep <= '9') {
+            int eval = 0;
+            while (*ep >= '0' && *ep <= '9') {
+                if (eval < 10000) eval = eval * 10 + (*ep - '0');
+                ep++;
+            }
+            dec_exp += esign ? -eval : eval;
+            p = ep;
+        }
+    }
+    if (endptr) *endptr = (char *)p;
+
+    if (mant == 0) {
+        return (uint64_t)sign << 63;
+    }
+
+    int bin_exp = 0;
+    while ((mant >> 63) == 0) {
+        mant <<= 1;
+        bin_exp--;
+    }
+
+    while (dec_exp > 0) {
+        uint64_t a_hi = mant >> 32;
+        uint64_t a_lo = mant & 0xFFFFFFFFULL;
+        uint64_t p_lo = a_lo * 10;
+        uint64_t p_hi = a_hi * 10;
+        uint64_t mid_carry = p_lo >> 32;
+        uint64_t lo = ((p_hi + mid_carry) << 32) | (p_lo & 0xFFFFFFFFULL);
+        uint64_t hi = (p_hi + mid_carry) >> 32;
+
+        while (hi != 0) {
+            lo = (lo >> 1) | (hi << 63);
+            hi >>= 1;
+            bin_exp++;
+        }
+        mant = lo;
+        while ((mant >> 63) == 0) {
+            mant <<= 1;
+            bin_exp--;
+        }
+        dec_exp--;
+    }
+    while (dec_exp < 0) {
+        mant = mant / 10;
+        if (mant == 0) break;
+        while ((mant >> 63) == 0) {
+            mant <<= 1;
+            bin_exp--;
+        }
+        dec_exp++;
+    }
+
+    int ieee_exp = bin_exp + 63 + 1023;
+    uint64_t no_implicit = mant & 0x7FFFFFFFFFFFFFFFULL;
+    uint64_t round_bit   = (no_implicit >> 10) & 1;
+    uint64_t sticky      = (no_implicit & 0x3FFULL) ? 1 : 0;
+    uint64_t frac        = no_implicit >> 11;
+    if (round_bit && (sticky || (frac & 1))) {
+        frac++;
+        if (frac == (1ULL << 52)) {
+            frac = 0;
+            ieee_exp++;
+        }
+    }
+
+    if (ieee_exp >= 0x7FF) {
+        return ((uint64_t)sign << 63) | 0x7FF0000000000000ULL;
+    }
+    if (ieee_exp <= 0) {
+        return (uint64_t)sign << 63;
+    }
+    return ((uint64_t)sign << 63) |
+           ((uint64_t)ieee_exp << 52) |
+           (frac & 0xFFFFFFFFFFFFFULL);
+}
+
+double strtod(const char *s, char **endptr)
+{
+    uint64_t bits = __cervus_strtod_bits(s, endptr);
+    double result;
+    __builtin_memcpy(&result, &bits, sizeof(double));
+    return result;
+}
+
+float strtof(const char *s, char **endptr)
+{
+    return (float)strtod(s, endptr);
+}
+
+long double strtold(const char *s, char **endptr)
+{
+    return (long double)strtod(s, endptr);
+}
+
+double atof(const char *s)
+{
+    return strtod(s, NULL);
+}