diff --git a/viperlib.vp b/viperlib.vp
index 4a8d1e3..36b7a9c 100644
--- a/viperlib.vp
+++ b/viperlib.vp
@@ -28,17 +28,23 @@ export def snprintf(buf: str, size: sizet, fmt: str, *args) -> int:
     ret: int = vsnprintf(buf, size, fmt, args)
     return ret
 
-# Check floating-point special values (IEEE 754)
-# Return: 0=normal, 1=+inf, 2=-inf, 3=nan
+# 检查浮点特殊值（IEEE 754）
+# 返回：0=正常, 1=+inf, 2=-inf, 3=nan
+# 注意：不可用位双关 `*&fbits = *&fv` 读取 IEEE 位模式——该赋值会被编译器静默
+# 丢弃（IR 中 fbits 恒为 0，见 TransPyV/output/db514c1af999c5f5.text.ll），会使
+# 本函数恒返回 0、特殊值检查彻底失效，进而让 inf 进入浮点格式化循环而死循环。
+# 这里改用纯浮点语义判定，不依赖任何位操作：
+#   NaN ：fv != fv 为真
+#   ±inf：fv - fv 得到 NaN（有限值得到 0.0）
 def _check_special_float(fv: double) -> int:
-    fbits: uint64 = 0
-    *&fbits = *&fv
-    if ((fbits >> 52) & 0x7FF) != 0x7FF: return 0
-    is_neg: int = 1 if (fbits >> 63) != 0 else 0
-    if (fbits & 0x000FFFFFFFFFFFFF) == 0:
-        if is_neg: return 2
+    if fv != fv:
+        return 3
+    diff: double = fv - fv
+    if diff != diff:
+        if fv < 0.0:
+            return 2
         return 1
-    return 3
+    return 0
 
 export def vsnprintf(buf: bytes, size: sizet, fmt: str, ap: str) -> int:
     if fmt is None: return 0
@@ -626,8 +632,11 @@ export def vsnprintf(buf: bytes, size: sizet, fmt: str, ap: str) -> int:
                     di = 1
                 else:
                     scale: double = 1.0
-                    while work >= scale * 10.0:
+                    # 上界防护：inf 会让 `work >= scale*10.0` 永真，正常有限值最多 308 次
+                    scale_guard: int = 0
+                    while work >= scale * 10.0 and scale_guard < 400:
                         scale *= 10.0
+                        scale_guard += 1
                     while scale >= 1.0 and di < TEMP_BUF_SIZE - 1:
                         d: int = int(work / scale)
                         if d > 9: d = 9
@@ -779,12 +788,17 @@ export def vsnprintf(buf: bytes, size: sizet, fmt: str, ap: str) -> int:
                         ptr += _step
                 exp10: int = 0
                 if fv != 0.0:
-                    while fv >= 10.0:
+                    # 上界防护：inf 会让下面两个循环永真（inf/10==inf、inf*10==inf）
+                    exp_guard: int = 0
+                    while fv >= 10.0 and exp_guard < 400:
                         fv /= 10.0
                         exp10 += 1
-                    while fv < 1.0:
+                        exp_guard += 1
+                    exp_guard = 0
+                    while fv < 1.0 and exp_guard < 400:
                         fv *= 10.0
                         exp10 -= 1
+                        exp_guard += 1
                 int_digit: int = int(fv)
                 if int_digit > 9: int_digit = 9
                 if int_digit < 0: int_digit = 0
@@ -971,12 +985,17 @@ export def vsnprintf(buf: bytes, size: sizet, fmt: str, ap: str) -> int:
                 fv_orig: double = fv
                 exp10: int = 0
                 if fv != 0.0:
-                    while fv >= 10.0:
+                    # 上界防护：卡死现场即此循环（inf 会让 fv>=10.0 永真，inf/10==inf）
+                    exp_guard: int = 0
+                    while fv >= 10.0 and exp_guard < 400:
                         fv /= 10.0
                         exp10 += 1
-                    while fv < 1.0:
+                        exp_guard += 1
+                    exp_guard = 0
+                    while fv < 1.0 and exp_guard < 400:
                         fv *= 10.0
                         exp10 -= 1
+                        exp_guard += 1
                 g_use_e: int = 0
                 if exp10 < -4 or exp10 >= precision:
                     g_use_e = 1
@@ -1029,8 +1048,11 @@ export def vsnprintf(buf: bytes, size: sizet, fmt: str, ap: str) -> int:
                         g_len = 1
                     else:
                         scale: double = 1.0
-                        while work >= scale * 10.0:
+                        # 上界防护：inf 会让 `work >= scale*10.0` 永真，正常有限值最多 308 次
+                        scale_guard: int = 0
+                        while work >= scale * 10.0 and scale_guard < 400:
                             scale *= 10.0
+                            scale_guard += 1
                         while scale >= 1.0 and g_len < TEMP_BUF_SIZE - 1:
                             d: int = int(work / scale)
                             if d > 9: d = 9