base: fix parse_number_f64("0.000...0001e30001")

Updates PR #184

internal/cgen/base/floatconv-submodule-code.c

diff --git a/internal/cgen/base/floatconv-submodule-code.c b/internal/cgen/base/floatconv-submodule-code.c
index 4b293f3..b162fc4 100644
--- a/internal/cgen/base/floatconv-submodule-code.c
+++ b/internal/cgen/base/floatconv-submodule-code.c
@@ -422,9 +422,15 @@
       p++;
     }
 
+    // (1 << 24) is both smaller than ((INT32_MAX - 9) / 10) and larger than
+    // ((WUFFS_BASE__PARSE_NUMBER_XXX__SLICE_LEN_MAX_INCL * 10) + 9).
+    //
+    // dp's magnitude is at most s.len, and so at most
+    // WUFFS_BASE__PARSE_NUMBER_XXX__SLICE_LEN_MAX_INCL. Any exp outside
+    // ±exp_large gives the same (infinite or zero) result.
+    const int32_t exp_large =  1 << 24;
+
     int32_t exp = 0;
-    const int32_t exp_large = WUFFS_PRIVATE_IMPL__HPD__DECIMAL_POINT__RANGE +
-                              WUFFS_PRIVATE_IMPL__HPD__DIGITS_PRECISION;
     bool saw_exp_digits = false;
     for (; p < q; p++) {
       if ((*p == '_') &&

release/c/wuffs-unsupported-snapshot.c

diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 71f03de..ad7e5f6 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -21832,9 +21832,15 @@
       p++;
     }
 
+    // (1 << 24) is both smaller than ((INT32_MAX - 9) / 10) and larger than
+    // ((WUFFS_BASE__PARSE_NUMBER_XXX__SLICE_LEN_MAX_INCL * 10) + 9).
+    //
+    // dp's magnitude is at most s.len, and so at most
+    // WUFFS_BASE__PARSE_NUMBER_XXX__SLICE_LEN_MAX_INCL. Any exp outside
+    // ±exp_large gives the same (infinite or zero) result.
+    const int32_t exp_large =  1 << 24;
+
     int32_t exp = 0;
-    const int32_t exp_large = WUFFS_PRIVATE_IMPL__HPD__DECIMAL_POINT__RANGE +
-                              WUFFS_PRIVATE_IMPL__HPD__DIGITS_PRECISION;
     bool saw_exp_digits = false;
     for (; p < q; p++) {
       if ((*p == '_') &&

test/c/std/json.c

diff --git a/test/c/std/json.c b/test/c/std/json.c
index 58e8fbf..450ad73 100644
--- a/test/c/std/json.c
+++ b/test/c/std/json.c
@@ -1123,6 +1123,47 @@
     }
   }
 
+
+  // Test long inputs whose large exponent cancels out the decimal point.
+  {
+    // Initialize buf to "0.000...0001e30001" and "1000...000e-30000" with
+    // 30000 zeroes. Both are equal to 1.
+    static char buf[30016];
+    const char* names[2] = {"0.000...0001e30001", "1000...000e-30000"};
+    for (int j = 0; j < 2; j++) {
+      size_t n = 0;
+      if (j == 0) {
+        buf[n++] = '0';
+        buf[n++] = '.';
+        memset(buf + n, '0', 30000);
+        n += 30000;
+        memcpy(buf + n, "1e30001", 7);
+        n += 7;
+      } else {
+        buf[n++] = '1';
+        memset(buf + n, '0', 30000);
+        n += 30000;
+        memcpy(buf + n, "e-30000", 7);
+        n += 7;
+      }
+
+      wuffs_base__result_f64 r = wuffs_base__parse_number_f64(
+          wuffs_base__make_slice_u8((uint8_t*)(void*)buf, n),
+          WUFFS_BASE__PARSE_NUMBER_XXX__DEFAULT_OPTIONS);
+      uint64_t have =
+          (r.status.repr == NULL)
+              ? wuffs_base__ieee_754_bit_representation__from_f64_to_u64(
+                    r.value)
+              : fail;
+      uint64_t want = 0x3FF0000000000000;
+      if (have != want) {
+        RETURN_FAIL("\"%s\": have 0x%016" PRIX64 ", want 0x%016" PRIX64,
+                    names[j], have, want);
+      }
+    }
+  }
+
+
   return NULL;
 }