1 files changed, 46 insertions, 13 deletions

diff --git a/gcc/ada/s-fatgen.adb b/gcc/ada/s-fatgen.adb
index 01bb2b44a97..be564cf6a0e 100644
--- a/gcc/ada/s-fatgen.adb
+++ b/gcc/ada/s-fatgen.adb
@@ -401,22 +401,37 @@ package body System.Fat_Gen is
    -- Pred --
    ----------
 
-   --  Subtract from the given number a number equivalent to the value of its
-   --  least significant bit. Given that the most significant bit represents
-   --  a value of 1.0 * radix ** (exp - 1), the value we want is obtained by
-   --  shifting this by (mantissa-1) bits to the right, i.e. decreasing the
-   --  exponent by that amount.
-
-   --  Zero has to be treated specially, since its exponent is zero
-
    function Pred (X : T) return T is
       X_Frac : T;
       X_Exp  : UI;
 
    begin
+      --  Zero has to be treated specially, since its exponent is zero
+
       if X = 0.0 then
          return -Succ (X);
 
+      --  Special treatment for most negative number
+
+      elsif X = T'First then
+
+         --  If not generating infinities, we raise a constraint error
+
+         if T'Machine_Overflows then
+            raise Constraint_Error with "Pred of largest negative number";
+
+         --  Otherwise generate a negative infinity
+
+         else
+            return X / (X - X);
+         end if;
+
+      --  Subtract from the given number a number equivalent to the value
+      --  of its least significant bit. Given that the most significant bit
+      --  represents a value of 1.0 * radix ** (exp - 1), the value we want
+      --  is obtained by shifting this by (mantissa-1) bits to the right,
+      --  i.e. decreasing the exponent by that amount.
+
       else
          Decompose (X, X_Frac, X_Exp);
 
@@ -624,17 +639,14 @@ package body System.Fat_Gen is
    -- Succ --
    ----------
 
-   --  Similar computation to that of Pred: find value of least significant
-   --  bit of given number, and add. Zero has to be treated specially since
-   --  the exponent can be zero, and also we want the smallest denormal if
-   --  denormals are supported.
-
    function Succ (X : T) return T is
       X_Frac : T;
       X_Exp  : UI;
       X1, X2 : T;
 
    begin
+      --  Treat zero specially since it has a zero exponent
+
       if X = 0.0 then
          X1 := 2.0 ** T'Machine_Emin;
 
@@ -648,6 +660,27 @@ package body System.Fat_Gen is
 
          return X1;
 
+      --  Special treatment for largest positive number
+
+      elsif X = T'Last then
+
+         --  If not generating infinities, we raise a constraint error
+
+         if T'Machine_Overflows then
+            raise Constraint_Error with "Succ of largest negative number";
+
+         --  Otherwise generate a positive infinity
+
+         else
+            return X / (X - X);
+         end if;
+
+      --  Add to the given number a number equivalent to the value
+      --  of its least significant bit. Given that the most significant bit
+      --  represents a value of 1.0 * radix ** (exp - 1), the value we want
+      --  is obtained by shifting this by (mantissa-1) bits to the right,
+      --  i.e. decreasing the exponent by that amount.
+
       else
          Decompose (X, X_Frac, X_Exp);