Intel 64 and IA-32 Architectures Software Developers Manual Volume 1, Basic Architecture

Vol. 1 4-29
DATA TYPES
When a numeric-overflow exception occurs and the exception is masked, the
processor sets the OE flag and returns one of the values shown in Table 4-10,
according to the current rounding mode. See Section 4.8.4, “Rounding.”
When numeric overflow occurs and the numeric-overflow exception is not masked,
the OE flag is set, a software exception handler is invoked, and the source and desti-
nation operands either remain unchanged or a biased result is stored in the destina-
tion operand (depending whether the overflow exception was generated during an
SSE/SSE2/SSE3 floating-point operation or an x87 FPU operation).
See the following sections for information regarding the numeric overflow exception
when detected while executing x87 FPU instructions or while executing
SSE/SSE2/SSE3 instructions:
• x87 FPU; Section 8.5.4, “Numeric Overflow Exception (#O)”
• SIMD floating-point exceptions; Section 11.5.2.4, “Numeric Overflow Exception
(#O)”
4.9.1.5 Numeric Underflow Exception (#U)
The processor detects a floating-point numeric underflow condition whenever the
result of rounding with unbounded exponent (taking into account precision control
for x87) is tiny; that is, less than the smallest possible normalized, finite value that
will fit into the destination operand. Table 4-11 shows the threshold range for
Table 4-9. Numeric Overflow Thresholds
Floating-Point Format Overflow Thresholds
Single Precision | x | ≥ 1.0 ∗ 2
128
Double Precision | x | ≥ 1.0 ∗ 2
1024
Double Extended Precision | x | ≥ 1.0 ∗ 2
16384
Table 4-10. Masked Responses to Numeric Overflow
Rounding Mode Sign of True Result Result
To nearest + +∞
––∞
Toward –∞ + Largest finite positive number
––∞
Toward +∞ ++∞
– Largest finite negative number
Toward zero + Largest finite positive number
– Largest finite negative number