Integer library routines (GNU Compiler Collection (GCC) Internals) (original) (raw)

3.1 Routines for integer arithmetic

The integer arithmetic routines are used on platforms that don’t provide hardware support for arithmetic operations on some modes.

3.1.1 Arithmetic functions

Runtime Function: int __ashlsi3 (int a, int b)

Runtime Function: long __ashldi3 (long a, int b)

Runtime Function: long long __ashlti3 (long long a, int b)

These functions return the result of shifting a left by b bits.

Runtime Function: int __ashrsi3 (int a, int b)

Runtime Function: long __ashrdi3 (long a, int b)

Runtime Function: long long __ashrti3 (long long a, int b)

These functions return the result of arithmetically shifting a right by b bits.

Runtime Function: int __divsi3 (int a, int b)

Runtime Function: long __divdi3 (long a, long b)

Runtime Function: long long __divti3 (long long a, long long b)

These functions return the quotient of the signed division of a andb.

Runtime Function: int __lshrsi3 (int a, int b)

Runtime Function: long __lshrdi3 (long a, int b)

Runtime Function: long long __lshrti3 (long long a, int b)

These functions return the result of logically shifting a right byb bits.

Runtime Function: int __modsi3 (int a, int b)

Runtime Function: long __moddi3 (long a, long b)

Runtime Function: long long __modti3 (long long a, long long b)

These functions return the remainder of the signed division of aand b.

Runtime Function: int __mulsi3 (int a, int b)

Runtime Function: long __muldi3 (long a, long b)

Runtime Function: long long __multi3 (long long a, long long b)

These functions return the product of a and b.

Runtime Function: long __negdi2 (long a)

Runtime Function: long long __negti2 (long long a)

These functions return the negation of a.

Runtime Function: unsigned int __udivsi3 (unsigned int a, unsigned int b)

Runtime Function: unsigned long __udivdi3 (unsigned long a, unsigned long b)

Runtime Function: unsigned long long __udivti3 (unsigned long long a, unsigned long long b)

These functions return the quotient of the unsigned division of aand b.

Runtime Function: unsigned long __udivmoddi4 (unsigned long a, unsigned long b, unsigned long *c)

Runtime Function: unsigned long long __udivmodti4 (unsigned long long a, unsigned long long b, unsigned long long *c)

These functions calculate both the quotient and remainder of the unsigned division of a and b. The return value is the quotient, and the remainder is placed in variable pointed to by c.

Runtime Function: unsigned int __umodsi3 (unsigned int a, unsigned int b)

Runtime Function: unsigned long __umoddi3 (unsigned long a, unsigned long b)

Runtime Function: unsigned long long __umodti3 (unsigned long long a, unsigned long long b)

These functions return the remainder of the unsigned division of aand b.

3.1.2 Comparison functions

The following functions implement integral comparisons. These functions implement a low-level compare, upon which the higher level comparison operators (such as less than and greater than or equal to) can be constructed. The returned values lie in the range zero to two, to allow the high-level operators to be implemented by testing the returned result using either signed or unsigned comparison.

Runtime Function: int __cmpdi2 (long a, long b)

Runtime Function: int __cmpti2 (long long a, long long b)

These functions perform a signed comparison of a and b. Ifa is less than b, they return 0; if a is greater thanb, they return 2; and if a and b are equal they return 1.

Runtime Function: int __ucmpdi2 (unsigned long a, unsigned long b)

Runtime Function: int __ucmpti2 (unsigned long long a, unsigned long long b)

These functions perform an unsigned comparison of a and b. If a is less than b, they return 0; if a is greater thanb, they return 2; and if a and b are equal they return 1.

3.1.3 Trapping arithmetic functions

The following functions implement trapping arithmetic. These functions call the libc function abort upon signed arithmetic overflow.

Runtime Function: int __absvsi2 (int a)

Runtime Function: long __absvdi2 (long a)

These functions return the absolute value of a.

Runtime Function: int __addvsi3 (int a, int b)

Runtime Function: long __addvdi3 (long a, long b)

These functions return the sum of a and b; that isa + b.

Runtime Function: int __mulvsi3 (int a, int b)

Runtime Function: long __mulvdi3 (long a, long b)

The functions return the product of a and b; that isa * b.

Runtime Function: int __negvsi2 (int a)

Runtime Function: long __negvdi2 (long a)

These functions return the negation of a; that is -a.

Runtime Function: int __subvsi3 (int a, int b)

Runtime Function: long __subvdi3 (long a, long b)

These functions return the difference between b and a; that is a - b.

3.1.4 Bit operations

Runtime Function: int __clzsi2 (unsigned int a)

Runtime Function: int __clzdi2 (unsigned long a)

Runtime Function: int __clzti2 (unsigned long long a)

These functions return the number of leading 0-bits in a, starting at the most significant bit position. If a is zero, the result is undefined.

Runtime Function: int __ctzsi2 (unsigned int a)

Runtime Function: int __ctzdi2 (unsigned long a)

Runtime Function: int __ctzti2 (unsigned long long a)

These functions return the number of trailing 0-bits in a, starting at the least significant bit position. If a is zero, the result is undefined.

Runtime Function: int __ffsdi2 (unsigned long a)

Runtime Function: int __ffsti2 (unsigned long long a)

These functions return the index of the least significant 1-bit in a, or the value zero if a is zero. The least significant bit is index one.

Runtime Function: int __paritysi2 (unsigned int a)

Runtime Function: int __paritydi2 (unsigned long a)

Runtime Function: int __parityti2 (unsigned long long a)

These functions return the value zero if the number of bits set ina is even, and the value one otherwise.

Runtime Function: int __popcountsi2 (unsigned int a)

Runtime Function: int __popcountdi2 (unsigned long a)

Runtime Function: int __popcountti2 (unsigned long long a)

These functions return the number of bits set in a.

Runtime Function: int32_t __bswapsi2 (int32_t a)

Runtime Function: int64_t __bswapdi2 (int64_t a)

These functions return the a byteswapped.

3.1.5 Bit-precise integer arithmetic functions

_BitInt(n) library functions operate on arrays of limbs, where each limb has __LIBGCC_BITINT_LIMB_WIDTH__ bits and the limbs are ordered according to __LIBGCC_BITINT_ORDER__ ordering. The most significant limb if n is not divisible by__LIBGCC_BITINT_LIMB_WIDTH__ contains padding bits which should be ignored on read (sign or zero extended), but extended on write. For the library functions, all bit-precise integers regardless of n are represented like that, even when the target ABI says that for some smalln they should be represented differently in memory. A pointer to the array of limbs argument is always accompanied with a bit size argument. If that argument is positive, it is number of bits and the number is assumed to be zero-extended to infinite precision, if that argument is negative, it is negated number of bits above which all bits are assumed to be sign-extended to infinite precision. These number of bits arguments don’t need to match actual n for the operation used in the source, they could be lowered because of sign or zero extensions on the input or because value-range optimization figures value will need certain lower number of bits. For big-endian ordering of limbs, when lowering the bit size argument the pointer argument needs to be adjusted as well. Negative bit size argument should be always smaller or equal to -2, because signed _BitInt(1) is not valid. For output arguments, either the corresponding bit size argument should be always positive (for multiplication and division), or is negative when the output of conversion from floating-point value is signed and positive when unsigned. The arrays of limbs output arguments point to should not overlap any inputs, while input arrays of limbs can overlap.UBILtype below stands for unsigned integer type with__LIBGCC_BITINT_LIMB_WIDTH__ bit precision.

Runtime Function: void __mulbitint3 (`UBILtype` *ret, int32_t retprec, const `UBILtype` *u, int32_t uprec, const `UBILtype` *v, int32_t vprec)

This function multiplies bit-precise integer operands u and v and stores result into retprec precision bit-precise integer result ret.

Runtime Function: void __divmodbitint4 (`UBILtype` *q, int32_t qprec, `UBILtype` *r, int32_t rprec, const `UBILtype` *u, int32_t uprec, const `UBILtype` *v, int32_t vprec)

This function divides bit-precise integer operands u and v and stores quotient into qprec precision bit-precise integer result q(unless q is NULL and qprec is 0, in that case quotient is not stored anywhere) and remainder into rprec precision bit-precise integer result r (similarly, unless r is NULL and rprecis 0).