test.c

int fast_trunc_one(int i) {
    int mantissa, exponent, sign, r;

    mantissa = (i & 0x07fffff) | 0x800000;
    exponent = 150 - ((i >> 23) & 0xff);
    sign = i & 0x80000000;

    if (exponent < 0) {
        r = mantissa << -exponent;                       /* diff */
    } else {
        r = mantissa >> exponent;                        /* diff */
    }

    return (r ^ -sign) + sign;                           /* diff */
}

int fast_trunc_two(int i) {
    int mantissa, exponent, sign, r;

    mantissa = (i & 0x07fffff) | 0x800000;
    exponent = 150 - ((i >> 23) & 0xff);
    sign = i & 0x80000000;

    if (exponent < 0) {
        r = (mantissa << -exponent) ^ -sign;             /* diff */
    } else {
        r = (mantissa >> exponent) ^ -sign;              /* diff */
    }

    return r + sign;                                     /* diff */
}

test.s

	.file	"test.c"
	.text
	.p2align 4,,15
	.globl	_fast_trunc_one
	.def	_fast_trunc_one;	.scl	2;	.type	32;	.endef
_fast_trunc_one:
LFB0:
	.cfi_startproc
	movl	4(%esp), %eax
	movl	$150, %ecx
	movl	%eax, %edx
	andl	$8388607, %edx
	sarl	$23, %eax
	orl	$8388608, %edx
	andl	$255, %eax
	subl	%eax, %ecx
	movl	%edx, %eax
	sarl	%cl, %eax
	testl	%ecx, %ecx
	js	L5
	rep
	ret
	.p2align 4,,7
L5:
	negl	%ecx
	movl	%edx, %eax
	sall	%cl, %eax
	ret
	.cfi_endproc
LFE0:
	.p2align 4,,15
	.globl	_fast_trunc_two
	.def	_fast_trunc_two;	.scl	2;	.type	32;	.endef
_fast_trunc_two:
LFB1:
	.cfi_startproc
	pushl	%ebx
	.cfi_def_cfa_offset 8
	.cfi_offset 3, -8
	movl	8(%esp), %eax
	movl	$150, %ecx
	movl	%eax, %ebx
	movl	%eax, %edx
	sarl	$23, %ebx
	andl	$8388607, %edx
	andl	$255, %ebx
	orl	$8388608, %edx
	andl	$-2147483648, %eax
	subl	%ebx, %ecx
	js	L9
	sarl	%cl, %edx
	movl	%eax, %ecx
	negl	%ecx
	xorl	%ecx, %edx
	addl	%edx, %eax
	popl	%ebx
	.cfi_remember_state
	.cfi_def_cfa_offset 4
	.cfi_restore 3
	ret
	.p2align 4,,7
L9:
	.cfi_restore_state
	negl	%ecx
	sall	%cl, %edx
	movl	%eax, %ecx
	negl	%ecx
	xorl	%ecx, %edx
	addl	%edx, %eax
	popl	%ebx
	.cfi_restore 3
	.cfi_def_cfa_offset 4
	ret
	.cfi_endproc
LFE1: