VM Spec

The Java^TM Virtual Machine Specification

f2l

Operation Convert float to long

f2l

Forms f2l = 140 (0x8c)

Stack ..., value ..., result.word1, result.word2

Description The value on the top of the operand stack must be of type float. It is popped from the operand stack and converted to a long. The result is pushed onto the operand stack:

If the value is NaN, the result of the conversion is a long 0.
Otherwise, if the value is not an infinity, it is rounded to an integer value V, rounding towards zero using IEEE 754 round-towards-zero mode. If this integer value V can be represented as a long, then the result is the long value V.
Otherwise, either the value must be too small (a negative value of large magnitude or negative infinity), and the result is the smallest representable value of type long, or the value must be too large (a positive value of large magnitude or positive infinity), and the result is the largest representable value of type long. Notes

The f2l instruction performs a narrowing primitive conversion (§2.6.3). It may lose information about the overall magnitude of value, and may also lose precision.

fadd

Operation Add float

fadd

Forms fadd = 98 (0x62)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack. The float result is value1 + value2. The result is pushed onto the operand stack.

The result of an fadd instruction is governed by the rules of IEEE arithmetic:

If either value is NaN, the result is NaN.
The sum of two infinities of opposite sign is NaN.
The sum of two infinities of the same sign is the infinity of that sign.
The sum of an infinity and any finite value is equal to the infinity.
The sum of two zeroes of opposite sign is positive zero.
The sum of two zeroes of the same sign is the zero of that sign.
The sum of a zero and a nonzero finite value is equal to the nonzero value.

The sum of two nonzero finite values of the same magnitude and opposite sign is positive zero.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, and the values have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using IEEE 754 round-to-nearest mode. If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, or loss of precision may occur, execution of an fadd instruction never throws a runtime exception.

faload

Operation Load float from array

faload

Forms faload = 48 (0x30)

Stack ..., arrayref, index ..., value

Description The arrayref must be of type reference and must refer to an array whose components are of type float. The index must be of type int. Both arrayref and index are popped from the operand stack. The float value in the component of the array at index is retrieved and pushed onto the top of the operand stack.

Runtime Exceptions If arrayref is null, faload throws a NullPointerException.

Otherwise, if index is not within the bounds of the array referenced by arrayref, the faload instruction throws an ArrayIndexOutOfBoundsException.

fastore

Operation Store into float array

fastore

Forms fastore = 81 (0x51)

Stack ..., arrayref, index, value ...

Description The arrayref must be of type reference and must refer to an array whose components are of type float. The index must be of type int and the value must be of type float. The arrayref, index, and value are popped from the operand stack. The float value is stored as the component of the array indexed by index.

Runtime Exceptions If arrayref is null, fastore throws a NullPointerException.

Otherwise, if index is not within the bounds of the array referenced by arrayref, the fastore instruction throws an ArrayIndexOutOfBoundsException.

fcmp<op>

Operation Compare float

fcmp<op>

Forms fcmpg = 150 (0x96)

fcmpl = 149 (0x95)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack, and a floating-point comparison is performed. If value1 is greater than value2, the int value 1 is pushed onto the operand stack. If value1 is equal to value2, the int value 0 is pushed onto the operand stack. If value1 is less than value2, the int value -1 is pushed onto the operand stack. If either value1 or value2 is NaN, the fcmpg instruction pushes the int value 1 onto the operand stack and the fcmpl instruction pushes the int value -1 onto the operand stack.

Floating-point comparison is performed in accordance with IEEE 754. All values other than NaN are ordered, with negative infinity less than all finite values and positive infinity greater than all finite values. Positive zero and negative zero are considered equal.

Notes The fcmpg and fcmpl instructions differ only in their treatment of a comparison involving NaN. NaN is unordered, so any float comparison fails if either or both of its operands are NaN. With both fcmpg and fcmpl available, any float comparison may be compiled to push the same result onto the operand stack whether the comparison fails on non-NaN values or fails because it encountered a NaN. For more information, see Section 7.5, "More Control Examples."

fconst_<f>

Operation Push float

fconst_<f>

Forms fconst_0 = 11 (0xb)

fconst_1 = 12 (0xc)

fconst_2 = 13 (0xd)

Stack ... ..., <f>

Description Push the float constant <f> (0.0, 1.0, or 2.0) onto the operand stack.

fdiv

Operation Divide float

fdiv

Forms fdiv = 110 (0x6e)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack. The float result is value1 / value2. The result is pushed onto the operand stack.

The result of an fdiv instruction is governed by the rules of IEEE arithmetic:

If either value is NaN, the result is NaN.
If neither value is NaN, the sign of the result is positive if both values have the same sign, negative if the values have different signs.
Division of an infinity by an infinity results in NaN.
Division of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
Division of a finite value by an infinity results in a signed zero, with the sign-producing rule just given.
Division of a zero by a zero results in NaN; division of zero by any other finite value results in a signed zero, with the sign-producing rule just given.
Division of a nonzero finite value by a zero results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the quotient is computed and rounded to the nearest float using IEEE 754 round-to-nearest mode. If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.

The Java Virtual Machine requires support of gradual underflow as defined by IEEE 754. Despite the fact that overflow, underflow, division by zero, or loss of precision may occur, execution of an fdiv instruction never throws a runtime exception.

fload

Operation Load float from local variable

fload
index

Forms fload = 23 (0x17)

Stack ... ..., value

Description The index is an unsigned byte that must be a valid index into the local variables of the current frame (§3.6). The local variable at index must contain a float. The value of the local variable at index is pushed onto the operand stack.

Notes The float opcode can be used in conjunction with the wide instruction to access a local variable using a two-byte unsigned index.

fload_<n>

Operation Load float from local variable

fload_<n>

Forms fload_0 = 34 (0x22)

fload_1 = 35 (0x23)

fload_2 = 36 (0x24)

fload_3 = 37 (0x25)

Stack ... ..., value

Description The <n> must be a valid index into the local variables of the current frame (§3.6). The local variable at <n> must contain a float. The value of the local variable at <n> is pushed onto the operand stack.

Notes Each of the fload_<n> instructions is the same as fload with an index of <n>, except that the operand <n> is implicit.

fmul

Operation Multiply float

fmul

Forms fmul = 106 (0x6a)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack. The float result is value1 * value2. The result is pushed onto the operand stack.

The result of an fmul instruction is governed by the rules of IEEE arithmetic:

If either value is NaN, the result is NaN.
If neither value is NaN, the sign of the result is positive if both values have the same sign, and negative if the values have different signs.
Multiplication of an infinity by a zero results in NaN.
Multiplication of an infinity by a finite value results in a signed infinity, with the sign-producing rule just given.
In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using IEEE 754 round-to-nearest mode. If the magnitude is too large to represent as a float, we say the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent as a float, we say the operation underflows; the result is then a zero of appropriate sign.

fneg

Operation Negate float

fneg

Forms fneg = 118 (0x76)

Stack ..., value ..., result

Description The value must be of type float. It is popped from the operand stack. The float result is the arithmetic negation of value, -value. The result is pushed onto the operand stack.

For float values, negation is not the same as subtraction from zero. If x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0. Unary minus merely inverts the sign of a float.

Special cases of interest:

If the operand is NaN, the result is NaN (recall that NaN has no sign).
If the operand is an infinity, the result is the infinity of opposite sign.
If the operand is a zero, the result is the zero of opposite sign.

frem

Operation Remainder float

frem

Forms frem = 114 (0x72)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack. The result is calculated and pushed onto the operand stack as a float.

The result of an frem instruction is not the same that of the as the so-called remainder operation defined by IEEE 754. The IEEE 754 "remainder" operation computes the remainder from a rounding division, not a truncating division, and so its behavior is not analogous to that of the usual integer remainder operator. Instead, the Java Virtual Machine defines frem to behave in a manner analogous to that of the Java Virtual Machine integer remainder instructions (irem and lrem); this may be compared with the C library function fmod.

The result of an frem instruction is governed by these rules:

If either value is NaN, the result is NaN.
If neither value is NaN, the sign of the result equals the sign of the dividend.
If the dividend is an infinity, or the divisor is a zero, or both, the result is NaN.
If the dividend is finite and the divisor is an infinity, the result equals the dividend.
If the dividend is a zero and the divisor is finite, the result equals the dividend.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the floating-point remainder result from a dividend value1 and a divisor value2 is defined by the mathematical relation

, where q is an integer that is negative only if

is negative and positive only if

is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of value1 and value2.

Despite the fact that division by zero may occur, evaluation of an frem instruction never throws a runtime exception. Overflow, underflow, or loss of precision cannot occur.

Notes The IEEE 754 remainder operation may be computed by the Java library routine Math.IEEEremainder.

freturn

Operation Return float from method

freturn

Forms freturn = 174 (0xae)

Stack ..., value

[empty]

Description The returning method must have return type float. The value must be of type float. The value is popped from the operand stack of the current frame (§3.6) and pushed onto the operand stack of the frame of the invoker. Any other values on the operand stack of the current method are discarded. If the returning method is a synchronized method, the monitor acquired or reentered on invocation of the method is released or exited (respectively) as if by execution of a monitorexit instruction.

The interpreter then returns control to the invoker of the method, reinstating the frame of the invoker.

fstore

Operation Store float into local variable

fstore
index

Forms fstore = 56 (0x38)

Stack ..., value ...

Description The index is an unsigned byte that must be a valid index into the local variables of the current frame (§3.6). The value on the top of the operand stack must be of type float. It is popped from the operand stack, and the value of the local variable at index is set to value.

Notes The fstore opcode can be used in conjunction with the wide instruction to access a local variable using a two-byte unsigned index.

fstore_<n>

Operation

fstore_<n>

Store float into local variable

Forms fstore_0 = 67 (0x43)

fstore_1 = 68 (0x44)

fstore_2 = 69 (0x45)

fstore_3 = 70 (0x46)

Stack ..., value ...

Description The <n> must be a valid index into the local variables of the current frame (§3.6). The value on the top of the operand stack must be of type float. It is popped from the operand stack, and the value of the local variable at <n> is set to value.

Notes Each of the fstore_<n> is the same as fstore with an index of <n>, except that the operand <n> is implicit.

fsub

Operation Subtract float

fsub

Forms fsub = 102 (0x66)

Stack ..., value1, value2 ..., result

Description Both value1 and value2 must be of type float. The values are popped from the operand stack. The float result is value1 - value2. The result is pushed onto the operand stack.

For float subtraction, it is always the case that a-b produces the same result as a+(-b). However, for the fsub instruction, subtraction from zero is not the same as negation, because if x is +0.0, then 0.0-x equals +0.0, but -x equals -0.0.

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